Family invites- cousins specifically

I need feedback (maybe not brutally honest feedback) but feedback. I’ve been engaged for (almost) 2 years now. We’ve been back and forth between big wedding/ elope/ courthouse and finally made a decision. We’ll be having a private ceremony with our immediate families (parents, siblings) in my brother’s backyard. A few months later we’ll have a “reception” / celebration with more people.
We’ve decided on no kids for a few reasons, (budget, venue size, rowdiness) so 21+ (with the exception of FHs sister who will be 18 and a bridesmaid)
Our venue holds 100 people comfortably with not much wiggle room. The majority of the guest list is family, aunts, uncles, adult cousins. The adult only factor leaves out 2 cousins on his side. And 2 of my side- simply for being under 21. The 2 not of age on my side are a group of 4 cousins (2 will be 21) BUT 1 of them I haven’t spoken to in over 5 years and the other I’ve spoken to once (when I got engaged)- I used to nanny these kids, school pick ups and doctors appointments, etc but we grew apart quickly as they got olderWe will be inviting the parents (aunts/ uncles) of those cousins, as well as cousins on the same side of the family.
I guess my long winded question is, for my 4 cousins in this scenario, do I invite the 2 who are 21+ but not their siblings? Or do I not invite that set of siblings all together?
Signed, a stressed out bride losing sleep over wanting to avoid family drama