Can I put 2 air conditioners in one line with 2 breakers?
Ummm, no, you cannot do this and there is no purpose it in anyway.  I'm going to guess that you have a dedicated 30A circuit for your 120V A/C unit.  That means that there is no more than 30A available on this circuit and the installed A/C needs that amount.

If you try to add another A/C on the same circuit (all code concerns aside) you will still only have the 30A available and there will not be enough available to power the 2nd unit.  So anytime both are operating the breaker will open.

What you need is a NEW 30A line from another 30A breaker in your box.  You mentioned that your box is full and that's a problem.

I suggest here that you need the services of a qualified electrician to see if the current box can be reorganized to free up some space for another circuit.  Otherwise the solution is likely to include upgrading your box to a new one that has more room.