Yizkor and Av Horachamim

R. Suiskind wrote: A.Were Yizkor Services said at all prior to WWII? Could you provide sources?

In Eastern Europe, and in congregations following Minhag Polin (for example Berlin and Hamburg), Yizkor was said on Yomim Tovim. According to Minhag Ashkenaz Yizkor wasn't said on Yomim Tovim, only on Shabbos before Shovuos and before Tisha B'av (the Shabbossos in which Av Horachamim is said), and in some congregations also on Yom Kippur.
You can see the two Shitos brought in Machzor Vitri, (Minhag Ashkenaz not to say Yizkor on YT, and Minhag France which later became Minhag Polin - to say). The Argument is if one is allowed to say a Kinnoh, a sad saying, on Yomim Tovim in which we have a Chiyuv De'oraiso to be happy.

R. Suiskind wrote: B. Av HaRachamim is said only Twice A Year? When did it become the general minhag to say every shabbos? Could you provide sources?

Only in Eastern Europe it became a Minhag to be said all around the year, maybe after Gzeiros that were there.

Michael FRBSH