I have a few questions

-Uncle Peter (Jones?) he the father of 2 daughters. Lana (mother of Daniel) and (?)
-What exactly makes him be Luke's (Sarah's husband) uncle?
-Is there a family tree featuring all of Daval's characters?
1. Uncle Peter is not Lana's father. This is just a rather speculative theory from long ago, which wasn't based on anything other than the fact that Uncle Peter's wife was named Maria, and that 'sounded' Spanish. Of course, this is based on the idea that both Lana and Daniel are assumed to be Spanish.
2. Uncle Peter is not Luke's uncle, at least not by blood. He's Sarah's uncle. Uncle Peter is Sarah's father's older brother.
3. Not a formal one, but here's all you need to know: in Immoral Desires, there's Lana, her son Daniel, her husband Alex, and her niece Sharon. In Satisfying Needs, there's Amanda, her son Liam, her sister Alexa, and her missing husband Thomas; secondary characters would include Mr. Lennon and his daughter Emma, and Mr. Dormund and his son Markus. In Together, there's Sarah, her nephew David, her niece Alice, her son Aaron, her Uncle Peter, and her husband Luke. And that's pretty much it. In the Uncle Peter comic, it's possible that Linda's husband George is Uncle Peter's biological son, making Linda his daughter in law. And that's as far as the family tree spans in my observation.
Of course, Daval3D created other comics under a different name, and if you want that family tree, you'll have to read the stories.