5yo problems

1) he wants to know what everyone said to everyone. If he leaves the room and I have a conversation with his sister he comes back and DEMANDS to know what I said. I tell him very politely that it doesn't concern him and I was speaking to his sister, not him. It doesn't work. 

2) he's horribly ungrateful. Today his mom surprised him with a children's vanilla steamer from Starbucks and he slammed it all in one sitting even though I encouraged him to enjoy it and sip t to make it last longer. He slammed the cup down and then yelled at his mother and said "mom this is ridiculous. Next time get me 2. This wasn't enough, I'm already done!" Her response was "oh okay honey"

3) His sister was playing a game and tried to hide from us to surprise us. He gave away her location and she cried. He laughed at her and refused to apologize. Seconds later he hid, I walked past him, he startled me and then he claimed I gave away his position and cried for half an hour 

4) he takes his sisters doll right out of her hands even though she's pretending it's her newborn baby and runs all around the house. She tries to get it back from Him and he grabs her and throws her to the floor and then doesn't apologize meaningfully - he isn't looking at her and he's laughing. A few seconds later she accidently steps on his foot and he stops dead in his tracks and yells "apologize!" She says sorry he replies "say it like you mean it!" And demands she apologizes again. (I've made him apologize twice before. He said sorry and I told him to say it again and he complained to his mother about it!) 

His mom works from home while I'm there and totally enables him and babies him but claims she'll always back me up when I punish him ....but the instant I try she defends him and says he's upset because his dad is out of town or his schedule was wacky today. But I'm sorry that doesn't mean he gets to be a rude and disrespectful little brat. What can I do to get him to behave?