I am in a similar situation. I am still young, and we do not have everything sorted out yet but am pregnant with baby number two. The way I see it is, everything else will get sorted but my babies having an immense gap for when we are 100% financially stable, or when we have x 100% sorted out and b 100% sorted out, then we will probably end up with a 6-7 year gap and I really did not want that.
For the time being I stopped going to school (they do not know that yet) and will be a SAHM (we are planning to move, and what I am studying I won't be able to use in that country), and am planning to continue once the kids are in school.
My family is highly against SAHM, they see it as lazy, sad etc. And so to tell them that plus about our second pregnancy, well it will be no party!
If you are genuinely happy about your pregnancy I would tell them if possible after your 12th week scan, and until then secretly enjoy all the things yourself, like the weekly photo's etc. So that you do not have to deal with the 'turbulence' of first semester and their possible negativity. This way you also have some time to adjust, absorb and get used to your pregnancy or else it might become too much.
Usually they do come around at least after when the baby is born, and if not too bad for them!