Divorce advice

Instead of your ex spending money on rent, he moves into the rental and rents out one or two rooms under rent a room giving him an extra rental income.
If the Ex is taking the younger child overnight, or planning to do so in the future, then renting out a room may not be an option.
 
If it's a 3 bed he still could rent one room. In addition if he only has the child on weekends he could possibly do a work week renting.