I WOULD MOVE THEM OUT OF OSCAR & PACU TANK FIRST !
I dont have any african clawed frogs, but I really dont recommend them being housed with these fish. I have oscars, and the pacu's are the same, they love to eat !
EVERYTHING ! I dont know how big or aggressive, yours are, but mine was 14 inches (the oscar).
Guppies are okay, because your frogs would eat them.
Anyway I would remove them into their own tank, his sore may be a BITE, thats getting infected ! Find out what you can put in his water for a wound thats infected.
Of course others may want to comment, and again I dont even keep these frogs, but I know Oscars !
You may want to ask Ginevive she keeps then and breeds them
Good luck hopoe he his sore gets better soon, :0(
Eve