(FWIW I know 2 Joshuas who go by Joe.)
Aside from that however, I do think they are a little too matchy matchy. I have identical twin girls and before we knew they were both girls (before anyone comments - they were DCDA twins so no evidence they were identical until we had DNA testing done post birth) we had picked names for 2 boys and a boy & a girl.
Our boys names both started with E and we had so many reservations about that. We stuck on them in the end because they were still very distinct names and would never have been shortened to anything like each other. (In fact - in the shortened versions only one started with E as the other name would have taken the second half of the name.)
Our favourite girls name alongside our favourite boys name was more problematic though as they both had the same ending when shortened and we really ummed and ahhed about it.
I have 4 DC, and without a doubt, the twins names are said together more than any other. I do think 2 matchy names would be a pain in the ass. My two are ID and best friends. They choose to be in the same class at school, have the same friend group and often like to coordinate their outfits (although I think this is more a girl thing than a twin thing), but their distinct names mean a lot to them. I do think it would be harder to form distinct identities with such similar names.
(I do recognise the problem though as we really debated giving up one of our favoured names if we’d had one of each, as the names just didn’t work together. And fwiw - I love both Joshua and Joseph!)