Yes, you do. If your wife and you are both on the title, you are both owners. One owner has no right to reduce the other owner's owership of or interest in the property without her consent. Currently, you would be 50-50 owners--your wife is half owner. If your parents are added, then there are 4 owners, so her interest is only a one-quarter interest. You cannot reduce her interest from 1/2 to 1/4 without her consent.
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