I don't see what the problem is with David and Joseph being his brothers' mns. I mean, you are always very set on "honoring" names, it seems almost obligatory that you honor somebody in your or his family by using their name.
But if you both don't get along with his brothers, that's something else. lol
I can't really see a modern guy named Abraham. I can't picture Abraham playing Little League, or joining the Boy Scouts, or getting a detention for shooting spitballs in algebra class, or having girls want to go to the prom with him, or any of those modern, ordinary, humdrum things modern guys do.
Katarina is very pretty asa first name. She could pretty much use any nn that Katherine might, though maybe not Kathy. Kat, Kit/Kitty, Kate/Katie, Trina, Trinny, Rina...