What you are purposing to do can be done. I have met husband and wife teams doing exactly what you are considering, but there are easier ways to keep the cruising kitty full of cash.
Charter yachts almost always need to operate out a specific location. Some countries are more friendly than others to mom and pop charter operations. Others are nearly impossible. You need a web site and booking people and advertisements in magazines to stay in business, and you have to be located where you can turn the boat quickly around between charters. The people I know doing this are working very hard to make it happen.
Often, you can achieve the same results with a lot less stress and work by doing part time work in your professions. For example, since your wife is a medical
professional, she could work for traveling nurses for three or four months a year, and the rest of the time you could cruise
. She could work part time in the US Virgin Islands
or Puerto Rico
as a medical professional.
I have cruised full time and part time, and both of them work really well. When you work part time, you keep up your professional skills and credentials, and you turn the cash flow on and off whenever you want.
In my experience, mixing work and pleasure by chartering your boat is doing things the hard way. Separating the work from the pleasure has always been easier and more enjoyable for me. When I work, I work. When I play, I play.