Unique Q--my husband's family is all over us...?

[lil sammy]

for hosting an exchange student. The problem they have is that we don't try for our own. We're 33 & 36, and financially stable. There is enough mental illness in my family line, that I've decided the buck stops here. My hubby agrees.
This is exascerbated by his sister just having 2 babies. I would like to present our point without revealing family demons. We are very happy with our choices and wish that they were as well. I don't want to sound like a wuss, but I don't want to be the villian here as I have been in many of his family bruhaha type things in the past. I don't fit or deserve that role.
Any advice or wisdom?
Thank you
No need for meds down there--just would appreciate advice on how to explain our choices to the inlaws. Maybe I worded it incorrectly or something...