I have depression and anxiety disorder. During my pregnancies, I wasn't able to take my meds, but the hormones (or something) lessened the conditions to the point where I was able to cope without meds for those nine months.
LMiment, it sounds like the other three are excited but also concerned. And it sounds like they're putting more stress on you by jumping all over you about everything all at once. As Willowstar said, ask them all to slow down and stop overwhelming you. There's a lot that needs to go into a pregnancy, but it doesn't all have to be figured out at once, and it isn't helping matters if they're throwing idea after idea and problem after problem at you.
As for how much weight you should gain during pregnancy... that isn't up to anyone other than a health care PROFESSIONAL to determine. The internet doesn't know everything.
Good for you for telling them about your pregnancy. You're gaining strength in the situation everytime you speak up for yourself. So keep speaking up, and know you have support here.
Me: 45, cis-het female, poly
Hubby: my husband, 42, monogamous
My daughters: Alt (age 20) and Country (age 17)
Guy: ex-boyfriend, occasional confidant