A joint-tenancy is a form of property ownership where all co-owners have an equal interest in the property, regardless of the individual owner's contribution to the property purchase.
This means that upon the death of a joint-tenant, his interest in the property will automatically pass on to the remaining co-owner(s), regardless of whether he has made a will.
You may read up more here;
And refer to the HDB site for more information;
Should you require any help in selling your property due to a demise of co-owner, feel free to reach out to us at hello@99.co so that we can connect you a most preferred agent partner who will be able to advise you better.