To whom should maftir be given. A Bar Mitzva boy who is not from the synagouge or a synagouge member who has Yahrzeit for his father in the coming week
The Biur Halacha (Orach Chaim 136) sets down the rules who has priority in regard to an Aliya to the torah. In principle a Bar –mitzvah boy takes precedence over a Yahrzeit. Although, the Biur Halacha does not specify Maftir for a Bar mitzvah boy, and other the other hand the minhag for maftir for a Yahrtzeit is an ancient one (See Shut =Responsa Rivash 115) it has become already a minhag that the chatan Bar- Mitzvah says maftir, so the order of precedence does not seem to change. On the other hand, a synagogue member takes precedence over a non member. If consequently, there is a situation of conflict your local Rav should be consulted to resolve the issue.