I told my parents the same day and in much the same way (in person, using more or less the same "script") as my wife did hers. The major difference was that for me it also involved coming out as bisexual, since that was the only way to make sense of my willingness to be partnered with a woman. We also couldn't find any resources for telling in-laws as such, so we just sort of adapted the "how to tell your parents" guides for trans people.
(Unfortunately, my mother promptly disowned me. Looking back, I'd've not bothered with the tremendous effort we put in, since she ignored it and rewrote her own history anyway! But she had long been abusive and manipulative, so a) not a typical response and b) not particularly distressing for me once I adjusted to the peace and quiet of not dealing with her.)
Good luck!!