Haha that's the only one I missed. I think it's because when I saw parent, I just started thinking about parents, and so grandparents never occurred to me.
A compound word is not a word with a prefix. Grand- is only a prefix in the genealogical sense; "grandstand" is a compound. Side (while it is a suffix in some cases) is never a prefix; both "sidearm" and "sideswipe" are compounds.
https://en.wikipedia.org/wiki/Biathlon
Bi should be accepted for the first one...
Pseudonym, false name