I had 4 attendants and DH had five, which was more than I would have liked and more than I intended.
I asked my sister, my SIL-to-be, and my best friend. My mother asked my cousin and I didn't feel like I could "uninvite" her. (Or, more accurately, my mother asked my aunt if my cousin would do it. My cousin has/had some pretty strong social anxiety. My aunt asked my cousin (insisted that she accept, actually), who called and said "fine, I'll do it." At that point I didn't feel like I could say "Um, well... no thanks." For the record, I really like my cousin, so I didn't have a problem with having her stand up with me -- but she *hates* that kind of stuff. She would have been much happier as a guest. She and I both know it.
My husband had more attendants 5 attendants and almost had six. His five were his three best friends and 2 of his cousins. He almost had 6 attendants because SIL's boyfriend practically insisted that he should be in the wedding, so DH added him. (He was in the program, we had a groomsman gift for him, etc.) Then he and SIL-to-be broke up a week before the wedding and he backed out. Sigh. After a very on-again-off-again several years, they finally got married and have now been married 15+ years (and have only threatened to divorce a couple dozen times. (Roll eyes.))
Anyhow, my mom thought it was just WRONG that we had an uneven number of attendants, but I didn't want more and DH didn't want fewer, so... there were were.