C.S.
C.,
Do you have a fiancee and a husband? Your January posts talk about your husband?
I don't understand your question. If your mother comes on vacation and isn't a hands-on grandma, it could be because she feels that is her vacation. It could also be because she doesn't live close enough to know your children's routines. It could also be because she feels she is the grandma and you are the mother and someone else is the father and she should have the grandparent fun while the parents do the care-taking.
As far as language goes, if your mom isn't comfortable speaking English, then that is life. It is not ignorant to speak in Portuguese but as Cheryl said, it is rude to speak in Portuguese around English-only speakers if the Portuguese speaker also speaks English reasonable well and is comfortable.
If your mom only visits a few times per year, make them short, orchestrated visits. Ask her to help and tell her exactly how to help with the children. Good luck!