Unless something has dramatically changed, you cannot use two metal pedals that have a common ground connection with a Yamaha keyboard. It caused a conflict when I tried them on the PSR series of boards because of the keyboard's floating ground connection. If the pedals do not have a common ground (ring) connection, there should not be a problem.
Good Luck,
Gary
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PSR-S950, TC Helicon Harmony-M, Digitech VR, Samson Q7, Sennheiser E855, Custom Console, and lots of other silly stuff!
K+E=W (Knowledge Plus Experience = Wisdom.)