If your husband doesn't 100% own all rental properties and you have been claiming as such, you should amend the returns since that's offside. Rental income should be claimed in proportion to the amount the property is owned.
IF you now became a co-owner in the property, your husband must claim a capital gain/loss on the proportion of the property that you now own.
So you don't have to amend previous returns to change ownership percentages, but you do have to claim capital gains to do so.
You do have to amend previous returns if you have been mis-reporting your proportion of rental income.