What to do when my stepson wont listen and dad wont step in?

I have a 7 year old stepson that has been babied most of his life because his parents were never married. He comes to visit on his weekends and stays part of the time with us and then with his grandma. The kid has figured out that if he bugs you enough or cries he WILL get what he wants. I tried to explain that as he gets older he wont be able to deal with his feelings because of this but no one will listen. I'm not angry towards the child of course but he needs to realize that crying doesn't get you what you want. We were told by his mom that he could get a puppy. We got him a very smart puppy that was almost completely potty trained as soon as he got here because he pestered us to death about it and cried. I would have made him wait a day or two so he would realize we are getting one but that's is not how you get what you want. He took care of the pup in his room and would wake me up if he did need to go out at night. We were so proud. Then he went to his grandma's house and she did everything for him and would put the pup up most of the day so he wouldn't have to play with it. When he came back to our house he wanted me to do it all for him. I wouldn't do it. His father was in bed sleeping and he works a lot so I couldn't wake him. The kid started crying like crazy because he didn't want to deal with the puppy. I told him to go to bed that he was overtired and we would talk about it tomorrow. So I took care of the pup. The next day he doesn't want to take it outside to play because there is no couch outside. I made him take care of him anyway and explained its a live creature not a game you can turn off and if he wasn't ready for all the responsibility he needed to tell us and it would be okay to make that decission. We encourage him to talk and make decissions. So we got the puppy a home the next day. Then He starts on wanting a Jack Russel or a monkey. I explained that pup would be the same as the one he gave up and that a monkey is more responsibility and cost like a lot of money. He said so, that his grandma could buy it then. I just told him that it wasn't right to ask that of her and why. Am I explaining things okay. His dad wont stand up to him and tell him no pets right now because he doesn't want to take care of it. His dad says maybe we would get him a smaller pet to take when he goes back home because then we wouldn't have to deal with it. Any suggestions? This child will not learn to cope and deal with feelings. He doesn't like to get up and do anything for himself. He thinks you are supposed to do it for him. I cant get his grandma to listen either. I hate it when he goes over there. She bribes him over with toys then he doesnt want to see his dad.