Doesn`t have to be a case of the kids choosing.
I split up with my wife last June and the one thing we did agree on is that we would put our kids interests first.
I have my kids 3 nights a week,by having them alternate weekends (Fri,Sat,Sun and Wed nights),they stay with their mum the rest of the time.
It works very well,kids seem happy and both myslef and the wife balance a decent amount of free time and quality time with the kids.
Best advice is for him to keep talking and find a solution that works for both.