The only part of it that makes sense is that they grew up together and did a paper route together. I get that. I had friends who lived in much more grandiose houses than my family had just right around the corner. And Derek Tudela was apparently an only child, and it's been my experience that parents of only children seem to "adopt" other people for their children to spend time with. My husband came from a big family and loved going to his only-child friend's house where they both got loads of attention, plenty of food, lots of things to do, etc. My daughter also had a friend like that and got to travel with the family while growing up, etc. Both kids get something out of it - one gets companionship, the other gets friendship plus the perks of being with an affluent family. Clearly Heidi likes kids since she runs a Day Care. So Justin and Derek as friends makes sense to me.
Beyond that it gets a bit fuzzy. All this defense of Justin and his family only makes sense if Heidi and her son are somehow implicated and believe they are in hot water up to their necks. Perhaps that's why both Tudelas seem so desperate to prove that the kidnapping is the only answer and LE is wrong.
I'm sure the police wondered why someone would be so willing to take in a whole family together when the DiPietros have lots of relatives living right there in the same town. One reason that comes to mind is access and insider knowledge. If they stayed with the Tudelas, then HT and DT would know exactly what was going on with the investigation and exactly what was on the minds of the various people, including Courtney.
And dragging AH, Heidi's cousin, into it early on was possibly more than just a chance to "help" Justin. Her blog and news articles was a way to "control" the story, which backfired because it only raised more questions about the stairs and gate, etc, but the meddling part might be self-serving if the Tudela family knows more than they are saying.
The insurance is obviously a major clue for LE. If the Tudelas knew Justin so well, then they knew he was basically unemployed. The story goes that Derek approached Justin, not the other way around, but how can we tell at this point what is actually true?