This is way, way too important and complicated situation to solicit advice from a message board. Get yourself some COMPETENT local help, somebody that can asses your overall situation.
Generally gifting real property is a bad idea. Your son may not be concerned with receiving gifted property with $0 basis but if he sells a few years down the road he will rue the day. There may not be a direct "gift tax" situation here but without knowing details about your personal circumstances it's impossible to make an informed judgement.
You might have your son manage the rental, (for an appropriate fee), and he may decide that he doesn't want the hassle with owning a rental either, but that means your husband doesn't have to deal with it anymore. Or, there are professional property managers, too.
I understand that gifting the property allows you to wash your hand of the rental hassle and seems like an easy way to solve the issue, but I'd bet there's a better approach.
