Here, I borrowed this list from
Metanorn, which will help in remembering the brothers and their respective ages:
Masaomi (age 31)- Oldest of the group, generic nice guy and a pediatrician. He’s also moe as hell.
Ukyo (age 28)- …The housewife of the brothers (he cooks and organizes everyone). A lawyer and the voice of reason.
Kaname (age 26) – A guy who likes hitting on girls, but is a monk of all things. He has a serious side to him though.
Hikaru (age 25)- The crossdresser of the family. Only, he does it for his job, which is writing novels. …I don’t know if that makes the crossdressing thing better or not.
Tsubaki (24)- Tsubaki is Azusa’s identical twin (he dyes his hair) and works as a seiyuu. He’s kind of a straightforward idiot and he totally has a fetish for imoutos.
Azusa (24)- Tsubaki’s identical twin and pretty much his complete opposite personality-wise. Meaning that he’s cool headed and pretty calm. Also a seiyuu.
Natsume (24)- Okay, I lied above. Azusa, Tsubaki and Natsume are actually triplets. Only, Natsume isn’t identical like Tsubaki and Azusa are (since he’s from a different egg cell), so he’s the odd one out. He doesn’t live in the same complex as everyone else and seems rough at first, but is a nice guy.
Louis (21)- Professional hairdresser. He’s kind of a airhead I guess?
Subaru (19/20)- The guy plays basketball in university and is SUPER awkward around Ema since he has 342092 brothers and zero experience with girls.
Iori (18)- A student who looks like a prince and is idolized by a lot of girls. Has issues.
Yusuke (16)- Yusuke was actually Ema’s classmate before he was her brother and he’s liked her since forever ago. A ~tsundere~.
Futo (14/15)- A rather popular idol who goes under a different surname for his job. Has an absolutely terrible personality.
Wataru (10)- The youngest of the brothers, a bit immature, but really close to Masaomi.
After looking at each one, I'd have to say that of all the brothers, Subaru, Iori, and Yusuke are really the only true contenders for the 16/17 year old Ema. All the others are either too old or too young. Futo is a possibility since his age seems to shift depending on adaptation between 14-15, but I just think he's too immature and not around enough to be an actual potential love interest.