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Something that has been suggested before, actually, and I think works well is this:
Instead of teleporting players, have them auto-path and auto-run to the summoner. This takes away all teleportation and 'sudden arrival' based exploits, and at first glance it looks like it would ruin the spirit of the thing, but if you look a little closer, a lot of people in the target demographic will have more time to AFK while they say, cook dinner, or deal with whatever else, which lets them get in position for content while they're able to actually play. It won't work for everyone, but it keeps the theme up, and it definitely helps with the teleportation-induced problems.
You'd configure it to take main streets to avoid mobs. Maybe have an optional icon that shows the player has no materials or such on them (if you keep that requirement) so they're less likely to get killed. Probably no immunity, but maybe you respawn at the spawnpoint nearest the summoner if you do get killed.
Suddenly it's a pain in the ass for little profit, to guilds, but still useful to most actual 'families'.