did Eddy and Adam get the idea to call Rumplestiltskin three times from Beetlejuice?

That's a possibility, though beetlejuice isn't the only character in fiction to use that summoning method.

No, I'm pretty sure they took nearly everything about Rumple from the fairytale 'Rumpelstiltskin.' So the reference to three times would probably be the three days he gave the Miller's Daughter to come up with his name. I believe, once she had his name, she also called it three times before he fell through the floor, although I could be mistaken. But, I'm not remembering a specific instance in which someone called his name three times on the show... What episode does this happen in?

Rumplestiltskin's story is 4,000 years old. 你 really think they ripped off Beetlejuice? Bwahahahahahaha. The Beetlejuice creators took much of the story from Rumplestiltskin.