The syntax will be:
ALTER TABLE <TAB_NAME> ADD <COLUMN_NAME> <TYPE>;
Repeat for each column.
If your new columns have NOT NULL constraints to them, you would need to create them with NULL allowed, update the rows then change the constraint to not null.
For deployment of the changes to all the servers.
It really depends on your infrastructure and your security policies.
If you have ssh to all 12 sites, you could have your deployment script on one of the servers and run it on every other ones from there.
If not, good old elbow grease would do it. 12 isn't a big number.
Don't forget to backup your database before applying the change.
I would actually include the backup in my deployment script and have a rollback.sql script to restore the backup just in case.