I'm not exactly clearing your personal circumstances, but I don't understand why the schedules have to be so complicated. In my case, the kids alternate weeks (7 days, switching on Friday) so they get almost perfect balance between us and our negotiations are minimal. Also changes to the schedule stand out like a sore thumb.

M39 D6 D3 (at S)
S 2014-09
D 2016-09

"You can't start a fire sitting around, crying over a broken heart" - Bruce Springsteen.