Absent forming a 501(c)(3) or similar vehicle those who "donate" to you can't take a deduction. You may find it difficult to receive sufficient donations to do anyhting useful. Given your business "model" you probably will not be able to get any reasonable financing on these properties.
Despite your noble causes, if you are employing people, you're likely going to have to treat them as employees. This means paying them at least a minimum wage, providing workmans compensation insurance, paying into the unimployment system, etc... Certain jobs are going to require licensed tradesmen and not unskilled labor. Even where not required, you're going to have to have some skilled person supervising your unskilled "vet" labor force.
You may not be allowed to have people residing in "distressed" properties if they aren't legally habitable under the building codes and ordinances.
If one of your vet workers / residents decides not to work, you're going to have to spend the effort to legally evict him (and boy have I seen that happen to people around here).