Translation:What is his name?
French has two words for "they" (ils and elles) based on gender too. I think that if a group has multiple genders or unknown genders, "ils" is used, and I think it's the same case with Japanese. The feminine version of they is uncommon because it can only be used for 100% female groups.
We can divide the groups of nouns that add お in front into two categories:
- お is customary. If お is not added it will not sound natural. e.g. おふろ, おさけ
- お is for politeness to the listener. This translates to "your" in English because English does not have this politeness concept. e.g. おとうさん, おたく
In this case 名前 falls in the 2nd category so if お is added it will sound unnatural (because it is asking for his name, not your name).