I submit the following story, from several years ago, as a discussion point.
It was my first birthday I would be celebrating since beginning to date the man who is now my husband (NH-then age 23). It was my 19th birthday, and he apparently felt obligated to make it special. I want to note that nearly all my birthdays after my eighth had been spent quietly with my family, aside from the 18th, which had been spent throwing water balloons (‘cuz that’s how I roll

) with my closest friends. Overall, I don’t consider birthdays a big deal once adulthood is reached (except maybe the 21st depending on the individual). I did not think to mention this to him at the time.
I was expecting something quiet with my NH; perhaps visit my parents, but low-stress and an early night. One of my dear high school friends happened to be in town on a school break on the day of my birthday and I made plans to meet up with him for coffee.
When I got home from that I discovered my NH had planned a surprise barbeque dinner party. Great, right? I looked around and realized that, although the guests were people I knew and liked, they were NH’s friends. No family and none of my personal friends. Then a latecomer showed up, and in tow he had a group of people with whom I had attended high school, and whom I did NOT care for in the least. I quietly (in another room) confirmed with my NH that the people of this particular group were gatecrashers who had attached themselves to an invited guest when they heard there was a party. The guest had agreed as he has a worldview that everyone should just get along, and the more, the merrier.
Fortunately, I get along well with most of NH’s circle and was able to mingle throughout dinner and dessert. Also fortunately no one brought gifts, I don’t know how I could have accepted gifts from people I liked but (then) hardly knew!
I felt distinctly uncomfortable with the gatecrashers, but due to the casualness was able to excuse myself to other parts of the house as needed when I felt uncomfortable. My impression was that they had thought this would be a different sort of party (drugs and alcohol--'cuz that's how they rolled

, per their own admission prior to this event), and were uncomfortable themselves. They ended up leaving just after the birthday cake.
I feel I succeeded at being gracious and polite, as most of the attendees continue to interact with NH and me. I later spoke to NH and requested no more surprise birthday parties. He agreed, and my birthdays have passed quietly. Holidays like Valentine’s, though, he continues to try to surprise me, but fortunately others are not invited to those occasions.
My questions are:
1-Is it all right to throw a party for someone and not invite that someone’s family or friends, but only one’s own? (For the record, NH had and has a good rel
ationship with my dad, and nothing inappropriate was happening at the party. I do believe his heart was in the right place but at the time I felt...hurt, for lack of a better word.)
2-If a guest of honor hadn’t known or liked the chosen attendees of a surprise party, would it be required that she stay and mingle? Or is it all right for her to stay a few minutes then plead “other plans because I didn’t know about this”? (This did seriously cross my mind at one point, when the crashers showed.)
3-If a guest brings uninvited people who either aren't known or liked by either the host or guest of honor, what is the eHell approved action to be taken? Should it be taken with the crashers, or with the one who invited them?
ETA Paragraph breaks--sorry, it seemed easy to read on my computer screen, but when I looked via my phone I can see how the breaks ran together.