What are the red pinkish shard things on the Ralts family’s heads/bodies? What do they do

Those are their horns, actually. Every member of the ralts family has crystalline horns that act as psychic amplifiers, much in the way that kadabra and alakazam’s spoons or spoink and grumpig’s pearls do.

This is why it’s generally considered impolite to downright dangerous to touch those horns.

Without permission, anyway.

(No, this is not an opportunity to “kinkshame” the people in the notes.)