Shrink/purge Huge transaction log - MS SQL 2014 Always on High Availability

I have a MS SQL 2014 Always on High Availability cluster with one primary and two secondaries. The transaction log sizes for the different databases has grown so large(3 TB), and the disk size cannot be extended beyond 4 TB. The DB is set up for Full recovery model. 

Now we need to reduce the transaction log size. Maximum log duration needed is one week. We need to reduce/shrink/purge these transaction logs with less performance impact and no down time.

I have used DBCC SHRINKFILE previously, but not sure this will lock transaction, block writes and hence a down time for customers.

DBCC SHRINKFILE (logfilename, EMPTYFILE)

Looking for suggestions on reducing the transaction log size without a down time for customers.