not sure I would ideally want to go two-up on a TTR250.
however, in Mongolia we came across various combinations of up to 3 individuals (rider + people or animals).
one time we helped out 3 herders on a 150cc bike with a flat tyre that they were stuffing with rawhide strips.
we bought Chinese grey import 150cc "sunik" bikes in Mongolia for about AU$750 and sold them after 5 weeks holiday.
total net cost about the same as a pair of quality handlebars back home.
the bikes had a really good luggage rack, a decent sized tank, good fuel economy, and didn't really fail us.
air filters fell apart instantly and had to be repaired with shoe glue. chain quality was pathetic (one broke).
also we couldn't register them (but no troubles with the law), and they were slow and vibrated.
but they did the job, including coping with mud and sand.
the country was great. nothing like an absence of fences to give a good feeling.
dunno what it would be like now - probably ruined by Australian mining operations!