They can and may do well but if one decides to be the dominant turtle then he/she can make life miserable for the others. I have a 30 year old ea. female eastern mud that was outside with a smaller female and a smaller male striped-neck. They got so scared of her they didn't want to go in the water anymore. I now have her in a 40 gal tank in the house.
Yes, they can hybridize. I have a female stripe neck/common musk turtle that is about 18 years old.