MySql Multi Master Active Active Mutli Write
1 &amp; 2) 
You should look at [auto_increment_increment] and auto_increment_offset variables. 
This prevents the two masters from creating the same Primary Key (assuming you are using Auto Increment Values).

3) 
Not Natively, for this you would need to look at moving to one of the Galera Cluster variants.

As it stands I wouldn't recommend an Active Active environment because you will almost certainly run into problems when the network drops out / replication stops on one or both sides.