The defending player, not you, chooses which creature blocks Fibrous Entangler.

Only one creature is required to block Fibrous Entangler. Other creatures may also block it, and are free to block other creatures or not block at all.

If Tangleclaw Werewolf transforms into Fibrous Entangler while it's attacking, having vigilance won't cause it to become untapped.

If each creature that could block Fibrous Entangler is tapped or is affected by a spell or ability that says it can't block, then none of them block. If there's a cost associated with having each of those creatures block, its controller isn't forced to pay the cost, so they don't have to block in that case either.