can we sell them to get money?
Well, you can release them, but you will get a little bit of gold only if they were in faction and you will loose a little bit of this faction rep. But this is not the most profitable source of gold, it is more profitable on later levels after Fuuka to go down the conveyor and just farm keycards and cyber restraints from mobs there and loot power crystals, when the crystals run out, just go down the conveyor belt at the same level and you'll end up at exactly the same level, where the crystals are untouched, and you can do this endlessly. You can sell anything to the Shopkeeper, including restraints, but the selling price drops with each sale, so it's best to sell only restraints there. Keycards and crystals are often can be sold to Nevermere, so it's better to gain and keep good rep with them.
also i want to know a good way to grind spell point.
It's simple here. Loot every chest that requires magic keys, orbs (but these ones costs reputation with the goddesses) and complete all the shrine quests on the level, since they give spell points or enchanted gear (which is expensive) as a reward.