Of course it's OK to have a trip with just you and your husband.  This year my husband and I will have one vacation where it's just us (skids will be with BM and our bio with my parents), we spent a week at Christmastime with my family at my parents' beach house with just our bio, and all of us will vacation for spring break week at a kid-friendly destination.  We could not afford that many vacations for all of us, and DH and I strongly believe that we need a week away for ourselves.  The skids go on vacation with BM and her husband, too, so it's not like they're missing out.

What is your custody situation with SD?  Do you have the ability to leave her with her mother so you can get away for spring break?  Is there a week in the summer where she can be with her mother so you and your husband can get away by yourselves?  I do think it's important for parents to spend uninterrupted time together without the kids, and if you can swing a vacation, that's an ideal way to do it.  The fact that your SD has mental issues and brings drama to your lives is more reason that you guys need a break.

Nothing wrong at all. Other than your DH allowing his prior relationship kid to detract from his marraige and family.

When it is his time with his kid then fine. But he should not allow SD to detract from his life and for sure should not allow her to detract from your life and the lives of the yound children  you share.

Go on vacation and make it crystal clear that DH will not ruin your trip together with pouty guilty daddy bullshit.

My DW struggled with this for a while.  She would get all morose when SS was on SpermLand visitation and would refuse to go on trips with me or family trips with my family if SS could not go too.  Finally I had enough and informed her that no longeer would I forego living and miss time together with just her or us with my family while SS was on visitation.

It took a couple of years after that for her to get out of her own guilty mom head and to actualy purge the mental BS over SS missing out and to enjoy our Skid free time.

You have to drag DH kicking and screaming on your adults only trips but it has to be done.

IMHO of course. 

Nothing wrong with it we do go away sometimes when we can afford it and do things without sd all the time. 

But we lucky that way because theres no custody agreements or anything bm not to far away. Never worked a day in her life.  We have sd fulltime. So we just drop her off at her mothers for a few days when we had enough. 

If no one likes it too bad. Because bm and sd do get there nose out of joint. But cant please everyone all of the time. 

I have never been on a holiday with the SDs and never would.  I once went on a weekend trip to MIL's place with them,  but it was a disaster, never to be repeated.   You have no obligation at all to do vacations with SD13, neither have you any obligation to mind her in the absence of DH.  Visitation is for her to see HIM, not you.  He needs to be there, or she doesn't come.  

We take trips both with and without both SDs (one lives with us full time, one does not). We take more trips with just us than with either of them. I think it's crucial for our relationship becaue it's crucial for my mental health.  

When DH and I were still dating we were invited to NC for Thanksgiving to spend the holiday with his family, I was all for it and couldn't wait. SS was not invited because we would be staying at my now SIL's BF house which was not kid proof or kid friendly not to mention the 10 hour car ride. Anyway I told DH not to tell BM we were going away, He did and BM INSISTED that he go with us, and how dare he take a trip to visit family without his son. I told DH that if SS was going I wasn't. I wasn't dealing with a child who had never been away from his BM longer than overnight and never that far away. He agreed so we didn' t go. My SIL was actually relieved that we didn't come with SS she knew how he was and that it would have ruined the holiday for everyone. 

My BF and I have taken 2 vacations together in our 8 year relationship. First was an overnight in NYC and skids cried because they didn't go. Then we went on a cruise 6 years later and they stopped talking to their dad for 3 months. It aggravates me when I try to plan a trip now with just him and I because he always puts it off, feels guilty for not bringing them. Mind you, we've taken them on 4 "family" vacations. Virgini beach twice NC and Washington DC. The skids never go on vacations with BM as she does not work and lives off of child support alone. Why do the skids feel that it is our responsibility to take them on these vacations. We both work and spend a lot of money on vacations and when we're on these vacations all they do is complain.  Don't feel bad for not taking the kids on a vacation. Everyone needs time away with their SO. And kids are just an distraction.