Open-source intelligence analysts reported that Crooks didn’t appear to use mainstream social media channels such as Facebook or Instagram and had an almost negligible internet footprint, which is highly unusual for a 20-year-old. Instead, analysts said that Crooks corresponded with friends and associates on a Discord server that they were now trying to access.
Discord servers are restricted ring-fenced sections of the internet. They are often used by gaming groups and communities as secure chat rooms but are also used by fringe organisations to push their ideologies and discuss wild conspiracy theories and plots.
I can't find any evidence of his family supporting Trump. Their local city councilor, a Democrat who recalled speaking with his parents, stated that the mother is a Democrat and the father is a Libertarian. He also stated the parents were pleasant and open to hearing his platform. Doesn't sound pro-Trump at all.