Can players at other locations play multiple cards to help you in combat?
After thoroughly searching, I think I found the answer in the FAQ's about encountering cards:


  Each player may play no more than 1 card of each type during each step; for example, no one player may play more than 1 blessing while attempting a check, though multiple players could each play 1 blessing during that check.


So in other words, no. Valeros could play 1 weapon to help, but not two. The rule is regardless of who is having the encounter.