Boat sharing is fabulous.
2-3 owners. Not more than that, as it gets too confusing. Legally most federations have standard contracts for exactly this. Use one of those, and tweek it to your likings.
Main reason for sharing is that the time spent servicing, is just much more fun when done with like-minded. As well is sharing all the experiences. U know that your partner wants the same fun as u. So an ear that actually listens to all your tales from the 7 oceans.
Besides, it is virtually impossible to use a yacht to its potential, unless u live on it. And then there is a risk that it becomes your bad conscious. Haunting u for not being there, taking care of her.
I have shared my boats for the past 15 years. Just great. Have fun
Share the cost, the sweat, the fun, the fuck-ups.