A.L.
So...they're so wrapped up with the child that died that they're neglecting the one that is left. That's intelligent.
Death of a baby is hard - I lost my only sister when she was a baby as well - but you need to let go of that one ('cause lets face it -SHE'S GONE) and care for the children that you still have left. It sound to me like he's trying to 'be' the baby so he will get the same attention that the now deceased baby is getting. It stand to reason that his parents are also so wrapped up in their support groups and grief that they're not discipling the way they should - hence the reason he's not listening. You need to have a frank talk with his parents and let them know what you've observed (including the cupcake incident...). I don't think his behavior will change unless something changes at home.