I'll tell when asked. Meaning: I won't lie. My family knows that we're trying again, but also that it isn't going as easily as the first time. My sister in particular knows that my last cycle was 80-some days, so it's not something that she can check in with me about every month. With 80 day cycles, you get a chance every 2.5 - 3 months!
I won't do a big production when I tell them. This will be our second kid. 5th grandkid on DH's side. 8th grandkid on my side.
They'll probably ask at Christmas and if so, I'll be honest, but I won't volunteer it.