I am a freemason and will be happy to help.
First, before he can join, he should be interviewed by 3 Brothers from the Lodge, they should interview him with you present so that you can ask any and all your questions and receive answers. They should ask if you support your husband/fiancee joining because if you do not, they should not allow him to Petition to join.
If you have any questions or concerns you can ask me via email if you wish. If you want to type the letter by the "ex-mason" or send a link to where it is, let me know and I can respond. there are lots of things out there by "ex-masons" and most of them are bogus.
freemasonry is a fraternity, nothing more, nothing less. it teaches a man that he should be active in his church and revere god, serve society, become a better man/husband/father.
anything you here regarding freemasonry and satan worship is absolutely false.
as i noted, the lodge should be willing to openly discuss freemasonry with you, if not then perhaps he is not looking at a legitimate lodge or perhaps there is a "bad" lodge out there - i do not know of anything, but the possibility exists.
JR provided some good links. another is freemasonry.bcy.ca you can find everything there as well.
and please do not hesitate to ask me.