Using pt-table-checksum to compare a slave's DB to another slave
If I'm not mistaken the pt-table-checksum uses report_host value to find slaves. 

May I suggest:


stop slave2. Note its current position.
Temporarily set up slave2 to replicate slave1 (binglog needs to be enabled on slave1)
Start only the io thread to get replication chain (i.e. start slave io_thread;)
Run pt-table-checksum from slave1
After check is done, stop slave and restore original replication on slave2 with saved position


This way you don't run the risk of messing up any slave.