Nothing wrong with wanting to take a trip with just your bios and their families. There's nothing to feel awkward about.  If your DH objects, he can stay home.

It's always awkward when my bios and steps are together, and more than once it has resulted in stupid drama. Better to do things separately for everyone's sake.

Who is paying for the trip? You mentioned that your husband has two adult children and there's one you don't want to invite.  Would you invite the other one?  Was the nightmarish drama on your other trips caused by his children, the interaction of the group, the size of the group or something else?  How does this put your husband in a terrible position?  Do his kids even have to know about the vacation (or that your kids are going) if he chooses not to invite them?  Does he recognize that his kids treat him like shit and don't have much of a relationship with you or is he blind to their faults?

In a vacuum, my inclination would be to tell him you're not willing to vacation with his kids because of your current lack of a relationship with them and the prior nightmarish vacation experiences, but you DO want to vacation with your own kids, and with him.  He can choose to go along, or he can choose to take a separate vacation with his kids.  Now, I'm assuming this is a vacation you and your kids can afford on your own.  If you're expecting him to fund the vacation for you and your kids while leaving his kids behind, that is a complicating factor.

Very expensive.  And very taxing, different personalities!   Just say NO to SD and the 8 of them. $400 x 8 and save the $3500 in tickets   I would not spend $8 to 10000 on them to be given a hard time making my vacation unenjoyable 

If DH doesn't like it he can go with them in separate rooms or even better separate hotels.  You can see them at lunch maybe  or maybe not. Those long lines LOL 

She chose to limit her relationship with you so why would she benefit from a trip?   You don't need to worry about her reaction, she has no say in how you spend your money.   
 

I never understood why grown children get upset about how parents spend their money....so entitled. 
Go with your family and make good memories.  Don't ruin their time over your SD possibly being upset.   Besides if you only talk to her twice a year, who says she has to know about the trip.

Go on a trip with your bios. DH can come along if he wants, or not. My mother has taken trips alone with one or two of us kids, without even the other bio siblings. Why does everyone have to be invited for everything? DH can take a separate trip with his kids alone if he wants.

"You will  not speak to me or to my husband in disrespectful terms.  You will no longer have a place in this family and will not speak to either me or my husband until you pull your head out of your rude disrespectful ill behaved immature ass. Now GTF out and stay gone until you fix your crap."

Lather....................... rinse....................... repeat.

Our dad made it crystal clear that his sons would not speak to his wife in anything but respectful terms and would behave towards his wife with absolute respect.  That she is our mother was beside the point.

A blended family marriage does not negate what should be this absolute requirement.

IMHO of course.

^^^100percent this^^^^what RAGS said.

You may decided to treat me like crap one time....I promise you I will not give you the chance to do it again. Your outta of here.

That is why we have wonderful vacations, cookouts, gatherings AND holidays. We dont put up with garbage from our kids or anyone else for that matter.

*my 1 adult kiddo pulled the ole, "IF YOU DONT WATCH your Grandchild so WE can go out, I guess you wont see your Grandchild again"

I said "Ok, I guess we wont see our Grandchild again. One more thing,,never use your kid as a pawn ever""

HOnestly I believe their heads popped off. It never happend again and snap they acted very normal.  I know a lot of adult kids use their kids as pawns and pull the you wont see your Grandkids again bs.

That is just one example of we dont play here. Nor should you.

How this ends UP is totally up to you.

My SD is only 12 but she also only turns up around holidays or parties. My husband came to agree with me that you don't get to only show up for the fun stuff. Family has to act like a family and do family things not just the fun things. So when sd12 refused to come to our house for regular visitation but began demanding vacations that was a very easy no for both of us. 

Yes this puts your husband in a difficult position if he is all about equality. But for these alienated step kids equality always seems to come out much more in their favor. 

There are ways to gently dissuade her and her family from coming on the vacation. The first way is for you to plan the majority of this trip with your kids before telling your husband or his kids. Try to plan it in a way that will make it difficult for SD and her expensive brood of six kids. You could pick a date that you know won't work for her or say that everybody is going to pay for their own transportation to Florida. For your kids and their smaller families this is a lot less of a burden than for her. 

Sorry to hear how this trip is going to turn out aside from the drama. If I'm counting right there are going to be sixteen people in total if all the kids and grandkids go? There is no way that you're all going to be hanging out together all the time. To be traveling with such a large group is pretty miserable! SD and her kids are probably going to go off and do their own thing at your expense. For someone that you don't even have a relationship with why would you want to spend so much money for them to not even be around you?

Your options are to take everyone and everyone will be miserable. Leave the miserable behind and everyone else can enjoy themselves. Or, no one goes.

I would go with option 2.

When those not invited complain, explain exactly whey they were not included.

Lather, rinse, repeat.

My SO and I are on a trip right now with my bio daughter and her boyfriend. My 2 other bio kids are not upset by this, they're busy doing other things this week. My SO has 2 kids that we would never travel with. I have no relationship with them and he doesn't have much of one. We would not enjoy traveling with them at all. 

I suggest you stop doing the large group, fully funded trips for the people you don't enjoy. If husband disagrees, like others have said, he's welcome to take them on a separate trip. Plan and pay for the trip YOU want, period. These are adults, they can find their way to their own family vacations if they're so inclined. You needn't keep funding them and ruining your own vacation.