Because they used to be humans, do 'normal' super mutants such as Marcus from FNV remember anything from being human? Or when they are exposed to the FEV do they adopt a completely new personality? And another quick question; are their life spans increased like Ghouls?

I think Marcus just says he forgot because it has been a long time, he says it in Fallout 2.

Complete memory loss of any prior life is the norm... but not all FEV-mutants experience the memory loss.

Exactly. Such as Lily and her grandkids.

Super Mutants created by the FEV from Maripsa does not make every human turned Super Mutant lose their memory.

Marcus for one and Lily is another. Marcus because it's been so long he can't remember and Lily got schizophrenia from using to many Stealth Boys.