Why would they need to deal with Peter's family?
A) Does he really even have any remaining family? His grandfather was fairly old during the flashback in the first movie. He may have passed on, and it didn't really seem like he had any other immediate family.
B) I'd imagine the whole Infinity War scenario is going to move pretty quick, so he may not have any downtime to pop over to visit his family.
C) Would any remaining family even recognise him?
D) He clearly either doesn't want to or is avoiding going back to earth. He's had the capability of doing so for quite some time now, but that he hasn't is very telling.
The Guardians will probably be a late-stage addition to Infinity War. Either they arrive during a showdown with Thanos on earth because they caught wind of it, or they show up to provide the Avengers with transportation to wherever Thanos is.
My best guess is that in Infinity War Volume 1 (or whatever) there's a battle with Thanos on earth and Thanos flies off into space and everyone's like "Well, crap. Now what?" and then Thor's all like "I know a guy" and the Milano shows up, then Infinity War Volume 2 is primarily in space.