Yes, one joint tenant can arbitrarily declare that ownership be changed to TIC. You may have to sue to partition the house by sale. See a local real estate lawyer about how to change ownership.
BTW, what's wrong with JTWROS? The only differences are that a TIC share in a house passes through probate (and pays probate fees) and that TIC shares can be unequal.
Tracey
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This is not legal advice and you are not my client. Double check everything with your own attorney and your state's laws.