You could try, it won't hurt, but don't hold your breath. DS potty trained when he was also 2.8 and I was pg (but not twins, and I had 5 months to go!). Had a failed weekend. A week or two later he said "I want to wear pants today" and he has only had about 5 accidents since (It's been about 18 months now). If your DS is ready, then it should be fine. It may not necessarily make your life easier for when the babies are here, because in my experience with DS "I need a wee" means, "I know I need a wee, right now, this minute, take me to the toilet right away". It took a while for him to go to the toilet/potty under his own steam. If I were you though, I'd give it a go and if it doesn't click, then leave it for a while until your DS wants to do it himself.
Am I mad?! DS is 2.8 not remotely interested in potty, will sit on it with nappy on but not bare bottomed. He will sit on toilet though so I was thinking to go straight to toilet training. Did half hearted effort last weekend he sat on the toilet lots of times for stickers but didn't do anything. Several wee accidents on the floor but in the end I was too worn out to carry on. I'm expecting twins in 3 weeks so obviously there will be a lot of upheaval for DS. He is also moving bedrooms. I think deep down I know I should leave it until things are settled (if they'll ever be 'settled' with 3 under 3's!) but DH and the childminder are committed to helping if we start this weekend. Do you think it would be a waste of time and extra stress I don't need ?!