You really really need to stress to them that it IS necessary, if for no other reason than to insure the taxes are paid correctly and on time before all three of you wind up loosing it.

Plus the hassle the other one or two of you would have to go through if something was to happen to one or two of you. The Government can find ways of taking it away if there is any kind of loophole at all, and the only way to keep that from happening is a will. heck Mom and Dad has a will and I am the only heir! that's just so the government can't get their foot in the door in any way shape or form.