My 奶奶 is about the same as yours, she only cares about herself and her money but husband and sons do not mean anything to her. But my 奶奶 may be worst than yours because she always pretending she cares for the family in front of her son but actually she wants is money money, she only say thing but never do things.
When my daughter was just born, she said she can take care of my daughter for me, in actual fact, she want to come to my house so that my husband will pay her $4000 per month. I don't trust her much so I still hire a maid but because I am working full tim, I let my 奶奶 come to my house everyday to make sure the maid treat my daughter right. But end up my 奶奶 always gossip to the maid about me and taught the maid how to tell lies to me. Luckily I installed a camera and recorded all the bad things of her. My husband was so angry and ask her not to come anymore, but then she ask my husband to give back all her money which she lent us to buy the unit. Since then we only she her in new years or special occasions, she want us to come home only because everytime we go to her place she gets money. I just can't believe there is such a mother on the earth. Nevethless, I even don't understand why my husband still treat her as a mother, as for me, I will forgot I have such mother.