Normal?

Hello all. Im new here and looking for some advice/support/experiences. I received my nephew through foster care in the middle of July. My sister suffers from neurological problems and mental illness and has had a downward spiral, some of the damage is permanent. After speaking with cps, foster care, and lawyers there is no intention of my sister getting her son back. There are several things that concern me that everybody just keeps brushing off. After I brought my nephew into my home I realized things were much worse than anybody originally thought. He will be 5 in January and my 3 year old son is bigger than he his. After speaking to his ped he has always been very small, my sister was and is the same way. I was told to give him whatever he wants to eat, but this child hates eating. I give him what he wants, but then says he doesn't want it. I have thrown away so much food and my children are upset because I cater to him. This has became a bit better, but meal time has became something I dread. If I don't make him something else he will purposely throw his food on the floor. His height and weight are not even on the growth chart so I have to make him something else. I know I am being manipulated, but what do I do in this case? He is also extremely attached to me. I found this a bit endearing at first, but now it has become a bit suffocating. I always reassure him I will be back for him after work and spend a lot of time with him. I keep all promises I make and never lie to him. I thought the level of anxiety he has when I'm not around would lessen after 3 months, but it has only became worse. I have recently caught him peeking on me in the shower and have to lock the door when I'm using the toilet because he will open it. I have tried explaining why he can't do these things but it is not working. He also always misbehaves when my attention is not on him. If I am cooking dinner he does something bad, if I am helping my daughter with her homework he does something bad, if I am trying to teach my son how to dress himself he does something bad. I know he wants attention, but it has become overbearing. If I ignore the smaller behaviors it escalates. My daughter has told my friend that I do not have enough time for her anymore. I try to spend the same amount of time with them each and do group things as well. He always has to interrupt and doesn't stop. I am not allowed to isolate him for timeout to stop this either. I don't know what to do. I have asked his social worker and they brush it off. He is so charming and acts differently when he is around others. I am very concerned about this, but nobody believes me that he is like this. He has also developed a strange attachment to his head start teacher. His interaction with other children has also improved but he still does some things that bother me. When I am watching he will be kind and share and play nicely. But there are times when he thinks I'm not watching he'll try to get the other kids in trouble. Some examples are he gave my son a toy then started crying and said my son took it from. He has thrown himself on the floor and said one of the other kids pushed him down. He has said he doesn't want to play right now then call to the other kids then cry to me the others are bothering him. He will not leave my daughter alone either. She is the oldest and the only girl and he insists on trying to play with her even when I have told him to stop. This happens several times a day. I have tried everything to stop this. I don't know what else to do. There are some other things he does like constantly having his hands down his pants and showing his privates to others. He also asks the same things everyday all day. Very obvious questions. 3 months later and every morning he still asks me if I am brushing my teeth while I am brushing my teeth. He also never stops moving. He runs everywhere and is constantly fidgeting. I know there is a lot here but I feel like there are problems that need to be addressed and nobody seems to be helping me. I feel like I'm failing.