From his FB profile it appears that Marko Petrovic lives in Sisak, Croatia. Given that, and his references to Lloyd Evans wife in the collective, I'd guess he's an in-law but that really is only a guess.
Evans has split the exJW community in half and left a trail of upset individuals in his wake - he's made lots of enemies. I won't defend his agressive, bullying form of activism for a moment but that doesn't excuse lobbing unfounded allegations of sexual abuse at him.
Making serious accusations like this in public rather than taking them to the authorities is poor form. If Petrovic has evidence to back his claims he should produce it otherwise he should shut up.