I did not read the entire thread, so this may have been answered.
1) Does the OP's son live with her? The DGD too?
2) Where does the mother live? How old is she? Does she work and/or go to school?
i'm the OP, so i will answer your questions.
DS, his GF and the baby all live with me. GF moved in when the baby was born. GF is 18 and in a high school for teen parents. she does not work. getting her to go to school is hard enough!
i will tell you that they are both being very responsible parents. they are learning together and have a very strong relationship.
DS has a good, loving, supportive (extended) family. GF's family is the total opposite.
all of this growing and learning, etc has been easier for my DS because of the family he was raised in. GF on the other hand has had so many changes, and is learning still. i can't express to you how proud i am of both of them!