So what is keeping you there if you hate it so much (FWIW, I'd hate it too). 

Your husband is a liar and a cheater and doesn't  help you with your shared baby. His children are mean to your baby.

Seriously, make an exit plan. 

Consult an attorney to see what your options are.

He cannot simply take your child away from you, many courts are very much on the side of the bio mother, especially with one so young.

When you were 24 you made some rash decisions, and have learned from them the hard way. You only had yourself to look out for.

NOW you are making decisions for two, and your little needs you to make them wisely. The person you married is a liar and a cheat. He is not helping you raise your child and he is not a good parent. He is a parenting fail. Do not yolk yourself further with this person! I almost never say exiting is the answer, but wow, this sounds realy bad, and love truly is not enough.

Some things to consider: depending on how long you have been with this *non-man* as well as your financial status (working/non working) you will be able to collect spousal support as well as child support should you leave this situation. This will help you to raise your child in a safe and healthy environment. And get on your feet so you can have a better life for yourself and your child.

Good luck and keep us posted!!

Are you close to your parents? If you have a decent relationship with them, now might be the time to ask for some help. You need to explore your options as far as how to leave this mess, and it will be much easier with some real life support. Start by contacting a couple of attorneys and find out where you stand legally. Did you sign a prenup? Do you have a job?

You have cause to leave him. He's a known liar and a cheat. He's a piece of ahit.

My cousin was in a similar situation however, she was not married to the guy but did live away from her family/support system. The guy was horribly abusive and did nothing for the baby. She was unemployed and he threatened to take the baby if she left. She sought out a lawyer for consultation. His advice was to run. He said get back to your support system and then figure stuff out or you could be anchored to one place indefinitely due to a custody order. So that's what she did. She waited until the guy went to work and packed whatever she could and fled the state. There was no court order so she wasn't in contempt. The guy filed for visitation. She breast fed the baby so he couldn't be separated from her until he was older. He had 2 visits with the child. He then met a new victim and popped out a kid with her and forgot all about my cousin and her son. When he filed for visitation they automatically got him for childsupport which is garnished from his check. He hasn't contacted her or tried to have a relationship with the child since. Maybe not the best advice but it got her out of a really bad situation.

Yes, as the others said, leave when he's not home and go back to your parents' home. Ask them to buy a plane ticket for you and the baby. 
 

The other option as others have said is to go to a domestic violence shelter. His threat to take your baby is abusive and meant to control you. 
 

He will not get custody of your baby, don't worry about that. Normally I'd say moving away from the father is wrong, but this guy and his kids are a danger to you and your child. Once you move, don't allow him to take the baby for a visit until there is a Court Order in place. 

Document all of his lies, his unwillingness to help and the fact that you provide all child care, the things his kids do and say, and his threats. Write it all down and don't let anyone find it. Then either move with your parents or to a domestic violence shelter, and consult a lawyer. Your best bet may be to move across the country to minimize his chances of getting more custody. If it works for the HCBMs we read about here, it will likely work for you. Once you are free of him, though, don't be a HCBM. Completely separate your life from his and only communicate minimally through email, a parenting app, or your lawyer. Start as fresh as you can and deal with him only as much as the court orders you to. 

Get help from your parents, or a shelter.

Your partner is a liar, cheat, bully and lazy arse. His kids sound awful too. How can he let them call your baby, their own half sibling, "ugly" ?? 

He's a loser. You and your son will be so much better off without him.

Please start making photo copies of all important paperwork. Start eye balling where everything is IF you can not go out an make copies. And/or When you find it, take screen shots with phone.

Bank info, account numbers, insurance info/account numbers, Birth Certificate, your's and babies., your marriage license.  Name, address and phone number where dh works, his parents names/addresses/his siblings names and addresses...Health insurance names, numbers/

IF you can, start taking cash back when you go to stores. Makes a stash. 20bucks here, 20 bucks there..adds up.

Hope this helps a little. Social services in your town is also there to help. Also a womans shelter.

Tried to mummy my kids and act like she was in a position of authority to answer me back regarding the parenting of my kids, i shut that down immediately. It took my husband probably a year and a bit to finally grow the balls and tell her that our kids had a mum who made the decisions regarding their upbringing and hubby 100% supported it.

sd was told by her dad she simply had no authority or place to mummy my kids or answer them back.

any man who lets his feral kids call his newborn ugly and turns a blind eye is a crap dad!!

BUT channel your in Oscar winning acting performance!  Do not let on to your DH or any of the skids what is in your mind.

Put all the pieces in place to make your escape.  (The prev posters have given great advice about resources and getting copies of documents)

Once everything is ready, leave silently without a word or notice.  If you want to make a dramatic exit, swallow that impulse down.  Just like with leaving an awful job, it is tempting to want to tell everyone off, but it is never a good idea.  Same with leaving this type of relationship.

I don't really have any advice for you, but OMG if me and DH had a baby together, I would NEVER want SD to be around them. I would NEVER trust SD to be near my baby, shes EVIL. everone on the outside thinks she is this "poor innocent sweet girl" OMG she is a lying manipulative, MEAN, malicious, thief. I will NEVER trust her, She is ALWAYS trying to emotionally/physically hurt EVERYONE around her other than those who fall for her tricks/cater to her every whim.