Kids in the wedding

So my fh has a brother who has 3 kids, a 5 year old girl, a 3 year old boy and less than 6 month old boy. ( We are a few years out from the wedding so I'm not super worried about the one being so young lol) Naturally with this being his neice and nephews, I wanted to put them in the wedding as the flower girl and ring bearers. My fh also has a step brother who has two girls, 6 and 9 and a boy who is 4.

I feel like having 6 kids in the car and wedding ceremony is way too many? But I don't want to leave out his step brother's kids ( honestly the step brother could probably care less it's his wife that I think would be upset)

I also wonder if it would look weird with 6 kids in the wedding and I only have a MoH and he has a best man and a groomsman?

I'm open to ideas anyone has to some how incorporate the other kids, I know they aren't blood related but don't really treat them differently than I do the other kids.