How to make grandmother and my sister come to terms with each other?

I am staying alone in my birthplace doing an office job managing my expenses and my grandmother lives in the countryside.my sister has gone to Canada for her higher studies and has been there for the last 3 years.i was planning to go there for my higher studies but got refused for visa so I am still here and she saved some money for my college fees if I went there and she gave some money to my cousin brother who she is staying with because he wanted to send money home to my maternal aunt.so the issue is my grandmother got mad at why she gave money to my cousin because she thinks my aunt doesn t need money right now but my sister says that she can t say no to my cousin because he helped her more with her fees .so now I am stuck as to what I should do here because this is a very tricky situation for me and I can t find a way to solve the problem without hurting either of the sides.please help me out guys thank you so much.