My sister an I,got in a phone argument and now she won't let me see my nieces.. but my nieces dad (they all live together) tried to set me up with a day to see the kids but she flipped out an I didn't get to see them this happened twice.the father will contact,me to come over an when I show up she,takes the kids into her room is,there
Anything I can do

Legally? No.

How about try and apologize to her and clear up the problem.

Yes - you can stop putting your brother in the middle, stop putting the kids in the middle, try to work it out with their mother.

Send your sister flowers and a card for Mother's Day from a loving sister who apologizes without any ifs ands or buts, regardless of whose fault the argument was.