Approaching 12 weeks how to tell the grandparents

I am 25yo paralegal my husband is a 28yo well-paid software developer. 
I simply do not know how to tell the  grandparents. 
When my MIL found out -inadvertently- that we were TTC, she told us we were too young . She had my husband at 35 or 36. We make much much more than she did when she had him. 
My parents do not think we should have kids ever. They both disliked being parents. I have 6 sisters and NONE of them have kids. Having children is to our family is what dropping out of college and stripping is to others. 
I don't know how to tell them...