Os freerolls são complicados porque muitos jogadores vão all-in
Just go as you should with pathological overbetters: never 3bet them pre or 3bet condensed, get your ranges tight and nut-heavy, and in case of huge all-ins your ranges should like for 99% contain nuts
Though as you are probably dealing with not just overbetters, but also maniacs, you should update your definition of nuts against these players, top pair good kicker can pretty much be considered pretty close to the nuts if your opponents constantly shoves middle pairs.
If the shoves occur preflop and you are sure that your opponent is a maniac (as there are weak players that can go shoving with big pairs, so proceed with caution unless you have seen them shoving multiple times in a short period of time), then:
1. With multiple callers only call with big pairs
2. If nobody called and most likely won't, you can call them with medium+ pocket pairs, medium+ aces and, if the player is completely insane and shoves every second hand, low aces could work too. You can also call with low pocket pairs, but in this case you will be flipping with 50% chance to double-up and 50% chance to bust.
If it is not a maniac and they shove rarely, just fold to their open-shoves. The same applies to the nits, who have very low (<10%) VPIP but who may open-shove strong hands.