I think you will be surprised. I started working recently too, and tend to come home past bedtime because of meetings or events at least once a week. DH had certainly done the bedtime routine in the past, but usually I was part of it too (ie I'd be nursing her and then he'd take over rocking her all the way down). I didn't try to plan it too much, because I figured it was something the two of them needed to figure out on their own. And really, they have quite easily. Bedtime takes a bit longer than with me, but it's definitely not horrible.
Does your DS take a pacifier or a bottle? If he's really attached to sucking as a falling asleep routine (mine is) then a paci might be the tool your DH needs to get him down. I'd suggest maybe doing most of the bedtime together, earlier in the night (like have everyone in pjs and brushed teeth etc by 7:30) so that your DH has more time to get everyone relaxed and in bed before they are too tired. Maybe the three of them can read in bed together for a bit, then your DH can leave the older one by himself with a book while he rocks the younger one? I think it's quite amazing to see how well kids can adapt to a change in their routine when they have a loving and responsive carer helping them... my kid surprised me with adapting so well to my DH taking over more of her care when I went back to work.