How small is this wedding?
I would definitely invite partners/spouses of siblings!
My guests would be........ First my parents, then my siblings, then their partners, and their children (and children's partners if they're old enough,) and any grandchildren my siblings have.
Then my husband-to-be's close extended family would come too. (OBVS!)
So that would be say, 25 to 30 people. Aunts, uncles, and cousins wouldn't get an invite, as my aunts, uncles, cousins, cousins partners and all their kids would make up over 30 people. (On top of the 25 I already have!!!) Ditto DH.
Then 5 - 10 friends of ours and their partners. So maybe 40-45 people. Not too many is it?