Sync Login PW across Multiple Instances
Logins are stored in master database. Since system databases cannot be part of AG (before sql server 2019 - From PASS summit 2018, MS announced that system dbs can be part of AG), they are not replicated by default.

The only way to do is to sync logins using sp_help_revlogin or use Late Robert Davis's script - Transferring Logins or use dbatools - Copy-DbaLogin (You can use -Force option, so that it will sync (drop and create) all the logins from source server to your destination server).