1st born successfully sleep trained but now have Irish twins

I currently work night shift (will move to 1st shift within a month) and my wife was pregnant with our 2nd. It was hard for her to sleep train our 1st born (currently 12 months). We successful sleep train her while i was in paternity leave, by controlled cry it out. It's been 3 weeks in and her sleep is doing phenomenal. She sleeps 10/11 hours at night 7pm to 5/6am with no wake and takes 2 naps, at 8am for about 2 hrs and at 2pm for about an hour could be less.

My question is how do we sleep train my new born when she hits that mark to sleep train? Do we put them in the same room, do we separate them?