i'm interested in apping someone who has another character in his head. would this be allowed? the other character wouldn't be appable at all

the character in question is tony stark from the ultimate marvel line, he has a sentient brain tumour/infinity stone at one point which manifests as a small boy. a similar example because that's really weird would be justice and anders from dragon age except tony's brain tumour can't take over his body and can't really interact with anyone except through technology