Your wife has no right to demand same Flat, as its not yours 100%. your Father has 50% shares in it and Your Parents has right to demand maintenance from you. no law will force you to give her same Flat.
As you do not have any issue with Your Wife other than FLAT, you can ask your Father about all your money (%) if he can able to pay. else you have to decide sell it or keep it for you and pay Fathers share. Dont ask Parents to look for other Flat, just tell them you need money to buy another Flat, if he can give your Shares.(%)