Repercussion's ability will trigger "whenever a creature is dealt damage" (C.R. 603.2c). It won't trigger more often if more than one source (rather than one) deals damage to that creature at the same time (C.R. 700.1, 603.2c; see also Sun-Crowned Hunters and this thread).
But if you control more than one Repercussion, their abilities will trigger separately from each other (C.R. 113.2c; see also this thread and this thread).
In this case, Grizzly Bears is dealt 2 damage, and Runeclaw Bear is dealt 3 damage (by Grizzly Bears and Zealous Guardian). As a result, each Repercussion will trigger twice, once for Grizzly Bears and once (not twice) for Runeclaw Bear, for a total of four triggered abilities.
Commander/EDH Decks:
BRG The Blood of Jund - Kresh the Bloodbraided BRG
WR The Blades of Goldnight - Gisela, Blade of Goldnight WR
But if you control more than one Repercussion, their abilities will trigger separately from each other (C.R. 113.2c; see also this thread and this thread).
For example, assume that—