good question, one i hope some one knows the answer to. i know in rune factory 3 you could hae people from the village along with you if your friendship/romantic rank was high enough, and of course bring monsters as well(not sure if you could do both though) hopefully this follows suit in tides, if any one could clarify that would be greatly appreciated :3
Check the images tab and look at the third screenshot. The player has some monsters tagging along while he's in a dungeon, they have clover icons above their heads and their faces show up on the three circles on the HUD. There are also other screenshots that show this. As for having other humans as party members, I don't know. In what I've played of the game, I haven't seen a 'recruit' button during conversations like RF3 had. Maybe it only shows up when you've reached the necessary relationship status or maybe it uses a different system.