Thank you ryabinkym and @vshklyarnik and Joseph and anybody else that may have replied and that I have not read yet. And Judy Golan.
There is so much info I received in the last few days and more to come, it is amazing. Once the whole story is built, I will send a detailed message for those that have the patience to read. I'm not looking for living relatives at this point, just building the family tree, but who knows where this will lead...
I was not making much progress in this side of the family till I was able to establish the spelling of my grandmother's maiden name. I always heard "Weiss" or "Vaiss'. When I established that it was "Wajc", then the dominos started falling.
The juicy part is that Serla Wroclavski married Gerson Wajc and had four children, one of them Rivka Wajc. Rivka married her mother's brother, Israel Wroclavski, and became Rivka Wroclavski. I think I heard this kind of story several times in this forum.
Rivka and Israel were my grandparents from the maternal side. So my great-grandmother Serla and my grandfather Israel were siblings ! I never met Serla, who died in Treblinka with her husband Gerson in 1942, but I had the happiness of enjoying the company of my grandparents Israel and Rivka for many years. (Israel passed away at the age of 97).
Thank you all again,
maternal side - WAJC, WROCLAWSKI, WAJNBAUM, LAUFER - Opatow, Poland
paternal side - KRIVOROT, LIPOVETZKI, YANKELEVICH - Bessarabia