A lot of patience. This is a huge thing for them to process, even if they had suspected something before, and even if they are accepting and supportive from the outset, you need to be ready for them to make mistakes, to slip up and to sometimes make things difficult.
More than that, this is going to be somewhat akin to a death for them, and they will need time to deal with that. There will be anger, resentment, denial, trying to bargain with you etc. Be ready for it.
Of course, all that might not happen - this is kinda the process most people who want to be supportive will go through, but your folks may have a much easier time processing it, either because they've mentally prepared themselves, or because the full magnitude doesn't hit them all at once, allowing them to process it in bite-sized chunks. Be prepared for the worst, hope for the best, and you should be okay.
Good luck honey.
~Simone.