From the little I know, it seems dual-weilding wasn't all that common, but you can find it in Spanish and Filipino Espada y Daga. Also in India where a hero was said to have used a pata in each hand to carve a way through his enemies. Chinese seem to have a trend in dual swords with the fame of butterfly-blades and dual sabers.
I don't doubt that some Chinese martial concepts filtered down into SE Asia, just as Indian martial arts did... perhaps the Thai did have some dual sword methods... I know in the martial arts Krabi-krabong they DO train dual sticks... I don't doubt that those could be training sword movements.
However I don't know if they carried their swords together or in separate sheaths, I'd guess the latter.
EDIT: This link
here may interest you...