[giantg2]

All of those can be done without being legally married, and many actually are.

In many US families, it's not uncommon to take people you're seriously dating on family vacations, or have them over for holidays, etc.

Some people who choose not to get legally married have a ceremony and/or party.

Some people who get married don't change their name. People who don't get married can change their name if they want to.