The art looks good but there should be some similarity for the chemistry of them being related it doesn't matter whether they look same maybe their way of interaction, thinking, personality or generally their attitude towards their brother let the mother trust her son while worrying a little bit while her sister sharing time with him in some related interest or similar hobbies like working out, Clubs, Street Food, Fashion, Movies or simply them enjoying each other company they're very comfortable and confident around themselves more than normal should be