Timing is important. You won't be riding South to Ushuaia May to Sept. Too cold. Think about weather, altitude and seasons. On a bike ... it's vital.

I would agree, getting another travelers bike would #1. save money #2 Most for sale are KLR650's or Suzuki DR650's ... both FAR better than trying to squeeze two onto a 250cc Chinese bike. Ain't gonna happen, at least not for long. And what about luggage?

Getting that bike into your name and getting the TIP squared away ... could present some hurdles. See Toby.

I assume you think you will mostly be camping, yes? Rather than Hotels?
Uh huh. Well, if you camp, you need more gear. On a 250 a smallish back pack each and a tail bag is about all you'll fit. You need a lot more.

Riding a 650 (like KLR or DR650) you can load up full sized panniers and top bag with everything you might need and more. And you can fit a passenger ... not luxurious comfort ... but can be done. (get a better seat!)

Also, keep in mind much of the Andean countries are at very high altitude. You'd barely make it up solo with no luggage on a Chinese 250 at 5,000 meters. Two up? You won't go higher than 2500 meters. NO POWER.

Since you rode a CBR1000, you surly know this?

If you wan't to go with 250's, get one each. NOT two up. Sure, for cruising two up round some Spanish beach resort or Thai beach town ... two up on a 250 is fine. Print shirt, shorts, flip flops ... hey! You're all set! Riding S. America is a bit different.

Low on funds? Maybe time to wire home for more?