Not sure when the books were released, but I read them probably in the 93-95 era.
- There were multiple protagonists in this series and the viewpoints jumped around.
- I believe there was time travel involved and that some of the characters were from different times and the times got blurred at points.
- There was a crystal involved
- Each shard of this crystal was imbued with powers which were kind of telepathic in nature and characters, good and bad, were trying to gather multiple shards.
- I believe (this could be wrong) that mentally speaking with wolves and getting their help was one thing that the protagonists did.
- There was a series of caves being explored as well with shards being scattered across time