Can I put my relative on title as joint tenant.
If I should die, will 100% ownership be passed down to him/her, not my spouse, and would there be any tax to be paid by the joint tenant.

If your relative is set up as a joint tenant with right if survivorship, then yes, full title passes to him/her when you die, regardless of what your will says. The advantage of this is that it keeps the property out of probate when you die. The disadvantage is that if you are the current sole owner of the property it will have to be retitled, and there may be gift-tax implications (depending on the value of the property) - any gift taxes would be bourne by you, not the relative you've given the gift to. Finally, when you die your half-value in the property would be included in valuing your estate, and depending on the value of your estate there may be estate tax implications that your estate would have to pay. Currently only estates in excess of $2M value have to pay estate taxes. But there are no taxes that the joint tenant would have to pay when you die.