Is the 19 month old the oldest or youngest? I was confused by your post.
Honestly, you could get up and out at 9am, and be back at 11am, have lunch then nap so you could do it on their schedule.
But first, I'd say that you are noticing that their behavior is off because they are tired, you think it's important they be on the same schedule, here is what we are doing, what are you doing, and what do you want me to do? You could shift to 2 naps if necessary, but I would tell them that typically a child at 19 months doesn't need those 2 naps, they are fine with a 12 lunch and 12:30-3pm nap, which leaves them up long enough to be tired but not overtired by bedtime.
But, you'll have to ultimately do what the parents want.