Two people, same last name, both have master's degrees

I am finishing my Master of Healthcare Administration and my husband is a Master Plumber. I would like to refer to us correctly in an email as "The Masters Ourlastname" but I'm not sure if it is Masters or Masters' or just Master's. Can someone please tell me what is correct? Thank you!

A master’s degree is so called because it is a degree held by someone who is a master (a person qualified to teach in university).

The word was subsequently used synecdochically to refer to the degree itself, so rather than saying only that someone is a Master of/in Arts, people also started saying that he has a Master(’s degree) of/in Arts.

The original usage, however, is still perfectly valid, as is obvious from the string of titles often appended to names in acadaemia: Hov1015, M.H.A. says specifically (if the abbreviation is correct, at least) that Hov1015 is a Master of Healthcare Administration.

So The Masters Hov1015son would be perfectly fine for your purposes.