I breastfeed my son while pregnant. My 2nd is due anyday and my son is now 20 months. I weaned him.off breast at 16 months. I decided to as he was eating enough and they become very sensitive, i thought it was the right time for us. His sleep was very bad and he always woke up just wanting it for comfort. If you are happy to carru on it's fine too, some people tandem feed
I wasn't able to nurse when I got pregnant. My supply took too big of a hit and I had to stop. Your milk changes when you have a new born so I would imagine nursing your older child might not work. I would check with your pediatrician and ask. I have also heard that nursing makes your uterus contract, with that in late pregnancy it might not be a good idea. Best bet is to check with the doctors!
Tandem nursing is amazing! As long as you and baby are happy, and you have no medical issues preventing it,there is no reason to stop nursing even after baby comes. A few nursing support groups to help with tandem nursing I found are the La Leche League (LLL) and breastfeeding mom talk. They are amazing