How to handle air condenser with garage addition
Moving the condensers to the back of the garage is not a hard job but it takes time. The refrigerant is pumped into the condenser and the valves closed. The line set is cut and extended, the line set should be purged with nitrogen while being sweated back together normally a gross leak check under pressure.
 the line set is pulled to a vacuum recommended 500um or below, and leak checked again.
Depending on your state electrical code you may need a electrician to move the service disconnect and possibly add a 120v receptacle (this can be added to the back of the garage also when it is wired. Once everything is connected power the unit up and a final leak check and probably top off the Refrigerant. 

Moving the condensers would be much cheaper than making the cut out in the wall and having them in an enclosed area like that would hurt their efficiency. 
Have I done this yes both for additions and installing the condenser further away from bedroom walls where the noise was bothering the owner.  It’s a full days work with a pre made pad and no leaks in the system many may do it over 2 days. The wild card can be getting the system pumped back down.

The cost of building around the condensers will far exceed the cost of moving them, after their useful service life is over trying to install a new unit in that cut out may just get you laughed at and cost many times the original cost to move.