I will be coming to visit a loved one's grave there on December 24th, and wondered if the rest room facilities would be open?

Yes they are and will be.. Atleast, that's been my experience everytime I've visited my family members.

They should be; 12/24 isn't a federal holiday. If you call 717-865-5254 between 9 am and 3 pm tomorrow they'll be able to tell you for sure.

I was there yesterday. I believe they were open.