Put your baby in a tiny, windowless room?  Hell no, this would be my hill to die on - just put your foot down.   Nothing wrong with twin boys sharing a room.  

Is also against codes for occupancy and fire safety.  Until he gets his head out of his ass the new baby will have to be next to you in your bedroom for as long as it takes for him to come to his senses. There will be no adult activities during this time that baby is in your bedroom.  

Husband can sleep in the shoe box if he does not agree.  Does this windowless room even have heating and cooling? 

Have a smokin' hot fireman come check over the house for safety and updating the fire /smoke/ co detectors. Innocently ask the fireman if a dectector is needed in the closet that hubby wants to make into a nursery. Make sure you know that his answer will be missus you can't use that closet for a kids room. Be sure idiot husband hears this. Continue the safety inspection of the other bedrooms and point out the one you will. Making into the nursery. Read over the requirements for having two residents in a room and if necessary for the twin boys they may have to bump older brother from his room if he has the largest so that they have the correct amount of space by code.  They can hang a divider curtain or arrange the furniture to allow some privacy for the twins in one room.  

problem solved. Everyone has a safe and suitable room. 

you are the woman of the house. You are the Queen. Now straighten your crown and start decorating your baby's room.  Have fun.  Do not be bullied.  This is your first child. Make it special. Ignore the idiot.  

https://casetext.com/regulation/pennsylvania-code-rules-and-regulations/...

Fire egress-

https://windowwellexperts.com/irc-codes/us/pennsylvania/

The baby may even need the middle size bedroom and the older boy take the smallest.  Otherwise baby stuff will be everywhere. Hubby will still have to sleep in his shoebox because baby clothes and equipment will be covering his side of your bed. 
 

Read around here.  You will learn a lot. Most of all how to stand up for yourself.  Be strong. Be safe. 
 

Well, he's thinking like the Father of Four and you are thinking like the Mother of One. He's right that in large families, the youngest gets the worst bedroom arrangement until the oldest goes to college (youngest of 4 here!) BUT, this is your first child, not your fourth, so it's understandable that you were looking forward to decorating a nice room for your child and are looking out for her interests exclusively. He's probably also worried that the twins will resent the baby if they have to share a room, but as the others said, the closet he wants to use as the baby's bedroom does not meet fire code to be a bedroom.

Are you guys in a position financially to expand that small windowless room to make a real bedroom? That would be a solution, too, but I know it may not be feasible.

Same sex siblings share bedrooms that's life.  My brothers shared a bedroom, SS17 and SS15 share a bedroom. SO is the youngest of 4 boys..they all shared bedrooms. These are all examples of 3 bedroom houses. The boys will be fine sharing a bedroom.  
 

SS15 has his own personal space in our basement with his computer/ Xbox/ recliner etc. now that he is older.

And if you think about a baby's sleep cycle, it will always be dark in the room with no windows! 
 

My BS13 and 16 get the largest rooms besides the master since they are the oldest and here nearly full time. SD11 gets her own room since she's the only girl and SS3 and SS5 share a room since they are close in age and here half the time. We've done by age in our house and it works. My BD20 is obviously launched so she no longer has a room here, we have some of the kids double up if she comes home to visit. Which isn't too often since she moved out of state. 

His kids can can share the big bed room.   New baby means thing change. New baby get treated better or equal to SK 

Oh hell no. I put my foot down on this one. You should too. 

We have 4 bedrooms upstairs. Office, playroom, guest room, and SD10 room. The office is directly above our master and closest to the Laundry room and bathroom. It may be slightly larger than SD room. She has lived in the same room for almost 3 years. No issues. 

When I told DH the office will be turned into the nursery, He freaked out. "The baby shouldn't have a bigger room than SD." "Teen girls spend a lot of time in the bathroom right?" "I don't want her to feel like she's unwelcome." These were his concerns. 

I made a list of points. 

1. SD is only with us half the time. 

2. A baby is going to have WAY more dirty clothes/cleanups/spills. 

3. For my convenience, and also potty training, Our baby will need to be closet to the bathroom. 

4. Supposedly, SD is clastrophobic & doesn't even use the actual toilet in her bathroom bc it has a "water closet". She always goes to the downstairs hall bathroom. 

5. If SD wants to switch with the guest room or playroom, so be it. But she will NOT have the office. Period. 

It's time your DH starts thinking about you being a mother and how he can help YOU. Also, with the age difference between our SKs and bios, our DHs will need to stop comparing. Newborns are totally different from teens, and it's unfair for DHs to even TRY to make that comparison. 

Adjustments will be made around the house, and that's just facts. It's not that SKs are "being replaced" but our families are growing and DHs need to be realistic about  considering EVERYONE in the family, not just his "first borns."

Hope this helps!

The twins can share a room....period! 

I was in the same situation my husbands kids each have their own bedroom when i asked him if i can have one of the rooms for the baby and his two daughters can share a room he told me the baby can share the room with his daughter but she is really messy so i was like no thanks so my son is 4 months now and his crib is in my bedroom . I never get to do a nursery or anything a first time mon would do.

Honestly with twins -- even if I had a spare room I would have had them share and kept the other room as a guest room. 

Your DH is crazy. I like the poster that suggested keeping the baby in your bedroom until he changes his mind -- no adult activites included! 

Are the stepkids with you full time or part of the time? Where is the office?

I would put the baby in the bedroom closest to yours. It's just more practical. if you have to kick someone out to do it then so what? If you're the one getting up in the night then it's your call to put your daughter wherever works best for you. Say you need a double bed and a crib in the new bedroom so you're not disrupting everyone else, and unfortunately the size of the office just won't accommodate that! 

Twins share a room, the eldest gets his own room, the baby gets the room closest to the MBR.

I would make everyone move just so there is no one who can claim superior ownership of a room over someone else or make a claim to being targeted as the only victim.

DH keeps his closet/office, etc....  

If one or more of the Skids are only part timers in the home, make one of the rooms the guest/visiting Skid room.  Go with a day/trundle bed for the part timer(s).

A home has to meet the needs of the FT residents and accommodate PTers as best it can.

As much as a prior failed family breeder may want to cater to a PT kid resident, reality is that they are only PTers in the home and family.  FTers take precedence over PTers.

IMHO of course.

It's essential to use the right food for your baby before sleep. For example, I had some meals for him every evening. I prepared very carefully using only the right ingredients and the proportions. He sleeps very well with no problems. For this, I am using a performant electric kitchen scale from https://www.vont.com/product/digital-kitchen-scale/. It's helping me every day in the kitchen, so it's a suitable helper. It's easy to use, and the design is fascinating. I got it from https://www.amazon.com/Vont-Beautiful-Measurement-Stainless-Batteries/dp.... The seller is a well-known one with good reviews. I think it could be an amicable solution to your problem.

Gosh. This is awful. You are the first time mum of course we would want the best for your newborn.

The twins can certainly share a room. Discuss the needs of a child and ask him what would feel if you were to live in this room?

The youngest can't speak doesn't mean he gets the least treatment

He's just thinking from his dad of three point of view.