I'm writing a fic and I'm not sure which to choose. Plus, the question also made me curious to see what you guys would come up with.

Although Doris seems physically younger, I find the thought of Doris going around calling Blowhole her 'little bro' amusing.

As a side note, it is very, very rare for a dolphin to have more than one calf at a time, but not impossible. I just wanted to throw that out there for anyone who chose the "twins" option.

I'm not trying to be judgmental but I think older siblings are smart enough to take over the world.

I don't know, Doris just has this "older sibling" vibe about her while Blowhole is being the silly little brother with his dreams of taking over the world.

Blowhole kind of... looks older? I have no idea why, I just think he'd be the older brother. Meanwhile, Doris, the younger sister, probably had to deal with his strange "take over the world ideas" when they were young and just rolled her eyes at everything.

I would have chosen Blowhole as the older sibling, but I have a small instinct in me telling me they're possibly twins since they look close to being the same age but there's probably a reason why Doris may look younger.

I feel like Doris acts more like a big sister and Blowhole acts more like a little brother. Granted he is a little brother who has finally gotten big enough to beat his big sister in fights.

Dr. Blowhole's voice actor (born 1973) is younger than Doris's (born 1964). But Doris seems to act younger, and her voice seemed almost teenagerish when she was trying to operate her brother's Segway. I doubt she's a teen, but I do think Francis is at least a few years her senior.

Thanks for all of your inputs!