A house bought jointly, with the wife also paying instalments: whose is it?

Ownership depends on the names on the title and the agreement between husband and wife, and the wife's contribution can be claimed as jointly acquired matrimonial property (harta sepencarian).
If the house is in joint names, both are owners according to the agreed shares. If it is in the husband's name but the wife contributed to the payments, that contribution is taken into account on divorce or death through a claim for jointly acquired matrimonial property. It is best to make a written agreement on each party's share and consider a hibah for protection. See Rights of husband & wife and Faraid.