Personally I don't think you are clingy, as new mommies we all have that fear. And when your instinct tells you something then you should listen. First off all, I would not feel comfortable leaving my child with someone who will drink alcohol when looking after the child. That can be done when and If my child is home safe at home with me. Routine is very important to a child. My biggest concern is when people ignore my wishes and instructions, I mean it is my child and not theirs. You gave birth to the child and not the MIL. I had the same situation where my MIL made reference to my son as her son. It did not sit well with me, she also wanted to stay with us after our son was born and I did not want that as I am very independent.
I also think that because it is the first grandchild that they feel that they should be more hands on. Also that it is their right to spoil them. We do not see my MIL often, but when we do see her then I try to stay out of the picture because my son only wants me and she does not like that.
I hope that you got it sorted and that you are happy with your decision. Things change when you have kids, people change, relationships change.
Good luck and just stay strong and grounded to your decisions.