I agree these three words should all be treated as rare.
The predominance of mausoleums over mausolea as the plural is much more pronounced in the iWeb corpus: 1377 to 97; and the News on the Web corpus: 1671 to 50. Admittedly, just after this suggestion was posted I saw mausolea in a quote from Mary Beard's latest book: "the ashes of most emperors and their families ended up in one of two huge mausolea". But as a famed scholar specializing in ancient Rome, it would be a surprise if she didn't use the Latin plural. It seems the vast majority of writers use mausoleums in preference to mausolea, and it's plausible that quite a few players might be unaware of the latter word.
In future these three words will be classed as rare.