Wilma just wants them in there to increase their bonds and become a closer knit team despite their want to not trust others. By doing so they would be unlikely to ever fall apart and with how strong they are together they would become a long term valuable asset to the guild.
well, if it's truly such an exeptional sword, it's probably another excalibur.... i don't want to se another sword like that... i don't need to relive that trauma...