Her reasons for delaying 50-50 are unreasonable, as dad's are perfectly capable of handling even 1 year old kids just as well.
His reason of getting more access for his kids so that he doesn't pay support is callous and selfish.
He will not get them more than 60% unless she is incompetent, so he better accept early on that he will be paying some kind of child support if he makes more money than her. He should let the mediator explain exactly how it will go down.
From my own personal experience in mediation, I clued in pretty quickly that any posturing and maneuvering around child support is completely pointless. The amounts are largely determined by federally establish tables, and are difficult to challenge. He won't lose his kids by being an idiot about it, but he won't get them more than 60% of the time either, so he may as well just drop it. Same thing with division of assets. All assets and debt gets divided 50-50 in most cases, and it is only in the exact nature of the split (who keeps the house, who keeps the pension, etc. etc.) that either party has any control over.
With that stuff in mind, I made my own focus in mediation to be about managing how much I would have to pay (or not pay) in spousal. It was a smart decision on my part, because by settling the non-issues earlier, I was able to focus more on that little golden egg of mine.
Bottom line is that your friend needs to pick his battles, and know where to give concessions so that he has enough bargaining chips set aside to get the things that are most important to him.