Sorting an IF statement to perform function for variable in same group in excel

I am trying to get something done in excel and its pretty simple but I need some help because I don't use the program much. So I am trying to assign bonus points to students who are in groups of 7, and the condition is that if each student gets over 70% on the weeks assignment everyone gets their grade boosted to 90%. I have a column that says Yes or No to whether each individual student gets the requirement, and I have one with the number of each students groups. I already created an if statement that writes Yes or No to whether each individual student has gotten over 70%, but what now I am trying to do is create another IF statement that says if everyone in X group gets over 70%, put Yes or No in column that asks whether everyone got over 70%. It seems simple enough but I don't know how to short by group in my if statement.