Husband wants to add wife to deed and add third party as joint tenancy what are fair percentages of ownership?

The third party should only claim the percentage they put into the property. Husband and wife's share should be divided 50/50.

For example Husband 40% - Wife 40% - third party 20%

Or Husband 20% - Wife 20% - thrid party 60%

Get the idea? Husband and wife share equally.