What do I do when mediation fails to give an adequate, fair schedule?

This question is on behalf of my fiance. He has been trying to get regular time with his 2 kids (10 & 14) but his ex always has some reason why he can't get them. This has been about a weekend a month except May where no weekend "worked" for her. They live 45 mins north, in MI (we're in OH). They went for mediation on Monday and he was basically told that the kids seeing their friends & other activities are more important by the mediator. He was granted every 1st & 3rd weekend (Sat & Sun-tried asking if I could pick them up on Fri so they would be here when he got home from work & he could have all of Sat with them but no go) plus a couple Thurs-Mon during the summer. Holidays are up in the air. He asked for a few weeks (not consecutive) but ex said the kids wouldn't want to be away from their friends that long. She also lied about some things during mediation like she always lies to him about why they are too busy and he can't come get them. She has used the weather (snow but not that bad) and sickness (a sinus infection w/10 year old) as an excuse a few times and Cub Scouts (which he does with his stepfather) and other activities most other times. He wants to get them next weekend (his weekend AND Father's Day) but 14 year old has a sleepover. So he asked if he could at least yet 10 y.o. son and she said no bc 14 would be upset then it was that he likes to play Playstation with one of the girls at the party (after he pointed out that the stepfather takes them on outings separately quite frequently... like car races where the 2 of them are all this weekend). There's more but I'm running out of room. My fiance is wonderful with the kids, always send them home with clean clothes, we've been together 3 years (getting married in April), I adore his kids, & they love me too. My fiance has a hard time speaking and thinking fast when he's nervous or upset so I know mediation was hard for him. Court would be too. What can he do?