I believe they're both male. I don't believe the previous owner that they're the same age, because one of the turtles looks considerably healthier (the one that tries to bite that is). Unfortunately I don't have enough space for a second tank, so I'll have to give away one of the turtles and that will take a while in my country. Is there any temporary solution in the meanwhile?
PS: the turtle that is being bitten has gotten much healthier in the past few months and some of the retained scutes are falling off. However she has these little holes in her shell
https://imgur.com/7M7s58F, did she used to have shellrot in the past?