I have a 200 amp breaker box in my house. I have a 60 amp breaker box running off that to a garage about 100 feet away. I also have 30 amp breaker box running from the garage to a 2nd garage 5ft away. I bought a welder that needs a 50 amp outlet. I need to add a double pole 50amp breaker for the welder. Is there any possible way that I can hook into the 60 amp box in the 1st garage to use the welder? I have 3 open spaces in an 8 space Square D box. It currently has: 1- 20 amp breaker w/4 outlets, 1 - 20 amp breaker w/4 outlets, 1 - 15 amp breaker that has 2 light switches, 1 double 20 amp breaker for an Air Compressor, and 1 double 30 amp breaker that goes to the 2nd garage. If I don't run the air compressor when I use the welder, would it be possible to hook it into the box? Will I run the risk of a fire or trip breakers? Or is there another way I can run it to make it work?

Sid...
Hard to be accurate here, but why not try it and see if the breakers hold?
If any of them do trip you may have to think about an upgrade...
Try to turn off as much as you can, I think you'll be okay as the load on your
Welder is likely 80% or less of the 50 amp plug rating.