Kids or no kids

Depending on how your venue is set up, you could have an area for the kids somewhat out of the way. You could also look into hiring a babysitter (or two, depending on the total number) to help wrangle the kids and keep them from being disruptive and in the middle of everything. I totally get the not wanting to have kids at the wedding-we’re not, but it works for us because there aren’t many young kids in our family. If there aren’t any options for babysitters, and you want your moms and sister there, you might need to be flexible.

I'm sure there is someone you could hire to babysit. Also foster moms can out in for respite time, so that someone else comes in and watch the kids. You have 6 months until your wedding they can find a sitter.

Adding onto PPs, does your venue offer any childcare options? Our wedding was at a hotel that had "summer camp" activities that children could be enrolled in. We had a no children policy at our wedding, so this was very convenient for parents to be able to pop in and see their kids on site.

View Quoted Comment Sadly no there isnt

Typically there are respite hours for licensed foster parents for these types of situations.

What about just allowing children of your immediate family? You should come to some kind of compromise.

View Quoted Comment Great advice. I totally agree. Someone may have to compromise one way or another, either try and find a baby sitter or have some kids, who are closer family members to you.
Discuss with your FH about options and maybe menton it to your mom and sister to see if they're able to be flexible too.

I know a lot of people are staying suggesting to get a baby sitter but she stated they don’t have anyone but family. Some people only want family to watch the kids. Maybe just family kids?

My friends and family have foster children and some have disabled children. We ended up inviting the children because it was more important to us to have those friends and family not have to spend the night watching the clock or their phones to have to go home.
I think it is fine to only invite your mother's children as they are your mother's children, they'd be your foster siblings. I think you should see if your fiance could compromise on only having those kids invited due to the circumstances.