Answer A: (not so serious)
Since you only banned silvered weapons, I present to you:
Dealing a whopping ONE (1) fire damage on a hit.Yay.
I know it's kind of a loophole since it simply uses a different kind of equipment than the banned-for-this-question silvered ones but hey. [If this fits your question you could also use any other magical weapon, since the immunity is exclusively to nonmagical slashing etc. damage.
Answer B: (fully serious)
Push em off a cliff. Your last sentence just states "immune to other werewolfes", while their description clearly states
From Nonmagical Attacks Not Made With Silvered Weapons [Emphasis mine]
So the fall damage that Werewolf B (indirectly) causes Werewolf A is not an attack and therefore fully hits. Whether it's an out-of-combat strength/athletics contest or in-combat the 'special melee attack' for shoving Werewolf B off said cliff is dependent on the DM but the result could be the same.
The same thing apparently also counts for traps, since they do not make "attacks" either
There you go, Werewolfes can indeed hurt each other, just not too directly.