Not sure the definition of family you're using (spouse, kids, parents, sibs, aunties, uncles, cousins, godparents, the whole tribe, some combo therein). That said:
I'm someone who has elected not to tell any portion of my family, with the caveat that if I ever dated seriously again, I don't think I could be with someone again at that level of intimacy who didn't understand.
15 some odd years ago I didn't tell my family because I thought of PTSD the same way I thought of an ear infection or cold (that's nightmares & shit, right? Passing annoyances) The rest I just thought was just me. Now that I understand much better? Lol. Well, they've gotten to know me over the past 15 years. Also;
- I know my family quite well, and it's not something they'd gel with
- It's none of their business, really.
Because whether they know or not, I'd still be doing the same durn stuff I've been doing for 15 years. The only difference is that I'm currently accepted as myself, and if I disclosed, I'd be constantly challenged. As I said somewhere else recently, I have a comfortable level of ridicule in my life.
It fairly blew my mind when I first came on here and met so many people whose families are completely in the loop. I think it's kind of cool, actually, just not something that could work well within my own family.
While I realize you're asking for suggestions on how to tell them, I just wanted to present one option (of many) available to you: Ie, not. Whom you choose to disclose to, or not, is entirely your business. I don't believe there's a right or wrong choice here... As different families equate to different versions of what best looks like.
As full disclosure of bias: I'm just PTSD.