Nothing, as long as your employers are fully aware and approves of it. In most areas of the US, employment is an at-will agreement between both parties. As long as you don't withhold that information during the hiring process or make them feel deceived, you have nothing to worry about.
But because of the at-will agreement they can still dismiss you without cause or warning regardless of the understanding you have. One day someone forgets to take their medicine, ends up being angry at you for a mistake or perceived lack of performance and you just gave them the perfect explanation.
But I have a feeling that you would have a hard time swinging those agreements in the first place. Why would your employee compromise, unless you are irreplaceable?
