EDIT to say sorry i should have put a coin or something for scale! These are very small like the size of a gnat, couple of millimetres.
We’ve put out glue traps for fleas and caught these. Are they definitely fleas? I’ve been bitten in this house intermittently for a few years usually around summer, since I don’t stay in this house permanently (it’s my dads - and he doesn’t get bitten and if he does he doesn’t develop marks, I get huge red itchy welts) then it’s never really been dealt with. We suspected bed bugs so treated for that 2 summers ago and I wasn’t really in the house last summer.
We DO NOT have pets, never have, and previous owner didn’t either apparently. We don’t wear shoes indoors. The downstairs neighbour is very dirty though and has a dog that to be honest is always itching itself lol. If these photos do look like fleas, could they be coming from downstairs? In which case how to even solve this issue?
Also I am not in USA unfortunately, I am in Scotland and idek if pest control has expertise on this sort of thing cause all the info I read is for people with pets.