All my grandmothers(2) and great-grandmothers(2) are called Bobby ________(last name). My nephew has nine!! grandmothers, great grandmothers, and great-great grandmothers and he still manages to call all of them Bobby___________ without anyone getting confused.
As for my Uncles and Tantas, they are older so we added the title until we were about 13,14 and then dropped it. My nephew calls his uncles and tantas by their first names because most are very young and can be his playmates.