Trinity and Revelation are a two book story arc WRT Renee and Kendra’s father and his wife and what they’re up to. That part of the story was way too big to put in Trinity in its entirety. The HEA for Renee, Jack and Galen was done in book one and Revelation had a standalone HEA for Kendra and her hero (Max de La Vega).
All that said – yes, they are related to the Cascadia Wolves series and yes, some of the backstory is defined in those books (like how the mate bond works, etc). So if you pick up book seven in an established world, you might miss certain things, though many have read it without the others and been fine, some read it and were like, “What’s up with this guy just falling for Renee in five minutes!