Is it possible to dual wield whips? How big/small would they have to be for it to be possible or effective?
To the first question, yes. You’ll occasionally find people dual wielding whips as performance art.
As to making them effective, they’re not. Whips don’t make particularly good combat weapons. They can be very visually engaging, which means they can be quite appealing on screen or in art, but they’re not efficient.
Let me get this out of the way up front: There are a few people who advocate use of the whip as a self defense tool. They’re not completely wrong. There are ways to use a whip as a defensive tool. It’s also worth recognizing that these are some of the best whip users in the world and they can kinda make it work as a weapon.
There are also people who hunt big game with bullwhips. The whip can be a very useful tool in controlling (and apparently killing) animals.
None of this will make it more useful against a trained, armed, opponent, however.
So, this gets into a decision for you:
If you don’t care about being strictly realistic, and you’re more committed to a flashy story, the whip is an excellent choice, particularly in a visual medium (like animation, film, or comics.) A skilled whip user can create some truly stunning visuals, and as I’ve said, whips are very engaging visually. A skilled user can make them dance, and that’s certainly one way to keep an audience’s attention.
If you’re more interested in keeping your setting grounded and gritty, a whip is probably the wrong choice unless your character is in a truly desperate situation and has no other options.
While not technically a whip, a character using a length of chain as an improvised weapon is entirely plausible, and dangerous. Not something I would recommend starting out with, but, certainly a reasonable choice if nothing better is available.
On a similar note, whips are one of the few times you can legitimately set a weapon on fire and swing it around. It’s not really going to make it more viable, but it will look more impressive.
The one strength of the whip is the intimidation factor. They’re difficult to track and appear to present a far more comprehensive defense than they really offer. This isn’t insignificant, especially when dealing with an untrained opponent, and is the one viable element about the whip as a self defense tool; you can use one to make yourself appear more threatening. This isn’t something I’d be willing to stake my life on, but, anything’s a self defense tool, if you’re desperate enough.
So, short answer, yes, but it’s not effective.