So it sounds like there was not agreement on 50/50 with the kids in mediation. It sounds more like a pissing match on who the better parent is. In that regards, the mediator did not stick to what is important - equal time for the kids with both parents. What did the mediator do other than listen?
It seems that you now are in for a fight that I never had to deal with - custody time with the kids.
Hopefully the status quo as it has been will be a big influence as to the courts decision on custody.