Would somebody be able to offer me lawful guidance... My companion has parted from her ex and the two of them own a house together,

Would somebody be able to offer me lawful guidance... My companion has parted from her ex and the two of them own a house together, they are both able to sell the house yet he's requesting to get his full store back on the house in addition to anything the house sells for... Would he be able? My companion is hoping to get everything 50/50 as she wants to track down another house.