My current house was abandoned for 2 years and it had animals + weed grown in the garage. The moisture damage had to be repaired and the smell because most garage floors are porous lasted for about a year but eventually went away.
Commit to solving this problem with outdoor space. Free yourself from trying to make this work in the garage. Garage set ups should be very temporary if at all. Do what you need to do to move them out, it's going to be better for you and for them in many, many ways. So many people solve this...