Can my mom pay for legoland hotel w het cc if shes not staying

Yes

Yes they can

Thanks its for my sons 9thbirthday

That's usually fine with most hotels. However you will still need a credit card during your stay. They will authorize $50 per room per day for incidentals. The authorization is removed at the end of the stay if you don't charge anything to the room.

Typically yes, most hotels are not concerned about where the money comes from