Needing some support :/

So me and my fiancé are TTC and his whole side of the family is thrilled about it. One of his sisters doesn't understand why we aren't waiting until we are married though. But how we see it is that it's mainly just a title. We have lived together for a year and I know having a baby isn't going to change anything at all, but it's still kind of a big out down. My fiancé has ALS and with that disease he could change for the worse any day which is another reason we are wanting a baby so soon. I told my best friend and she wasn't that supportive and I know no one on my side will be supportive in my choice.... It's being a real out down and is making me not want a baby because no one seems to be on my side about it... Any advice?