At what time your older one goes to sleep? If 12:30 I agree it would be great to put them down at the same time. To keep second nap as it is I would cap the morning one even more, let's say to 20min.
Or as you said you can push till 1pm. I would do it gradually, 15min every couple of days so they get used to. Usually kiddos at that age are "used" to be tired at certain moment and they show all tiredness signs and they need couple of days to get used to new routine:).