My two can be exactly the same at times, so will be watching this thread for ideas...

A couple of things that I have done that have helped are:

Go outside - for some reason my two don't fight nearly as much outside as they do inside. As its hot now, first thing in the morning outside, even eat brekky outside. They burn some energy, do messy play etc. I also take them outside around 4pm as well.

Move bath time - bath time after dinner was just hyping them up. They now have a bath before dinner. Eat dinner then we all sit down for quiet time. If one of us parents is running around cleaning up etc just seems to hype them up. I do let my eldest child watch TV at this time. She just tends to sit and watch the TV so is actually using it to wind down. That leaves the 15 month old to wonder around or read books. Then they go to bed.

Also with the bath time moved I am finding I can get them to bed much earlier. At the moment they are both generally in bed asleep by 7pm. 3.5 y/o doesn't have a day sleep and 15 month old is on 1 sleep a day.