Since you have 2 children near the same age I have found it really will not work to have them on 2 different schedules. They both need to do the later bedtime. Put dark shades and curtains in his room so he won't know it's morning yet. But if you are getting her up to go to school in the fall there is no way he will be doing a different schedule than her.
It's too bad he is done with naps. That would solve the issue. Some kids just do not fit the cookie cutter shape we want them to fit into. Sounds like he is just not tired and is not going to go to sleep on command...lol.
I still enforced nap time at this age. I worked a lot of years in child care and some pre-school time too and I know that kids still need naps or at least a formal rest time in the early afternoons for their body to work at their peak. They just don't get restored very well if they go all those hours without laying down and taking a break.
We would lay down on the couch and watch a movie sometimes. It occupied their minds but their body was able to slow way down and get some rest. They didn't have to go to sleep but the did have to lay down and do something each afternoon.
They still take naps in kindergarten until after Christmas Break. Because it is still required. They don't have to sleep but they do have to rest and be quiet. If they schools make the kids do it at age 5 you know that it is still important to do for your 2, 3, 4, and even 5 year old child.