A recent client needed a bit of advice -- she owned a piece of property with some other family members, and she wanted her share to go to a different family member than the one she owned the property with.
Would her will allow her to do this? No, because the deed stated "joint tenancy" -- if any one of the joint tenants dies, the remainder of the property is transferred to the survivors. What she needed to do was have the property titled a "tenants in common" -- each party has the right to alienate, or transfer the ownership of, her ownership interest. This can be done by deed, will, or other conveyance.
As always, when dealing with legal issues it is always best to consult a legal expert for advice on your specific situation. Laws vary state by state, and from year to year depending on legislation.