We foster dogs and currently have 6…SIX…dogs. All on my couch watching family feud right now. I have never, and I mean NEVER, met or had a bad dog. Never had a bad horse either. They are all products of their humans. If he's as friendly as you say, he's worth keeping. The shelters are over run with animals that have been discarded. It's not place for a dog. They are a necessary place and resources are limited. The dog didn't pick his lot in life and if you have the means to help him out with some stability, then why not?
That said, you are under no obligation to take him in and frankly, neither is the old man's son but life happens and sometimes we gotta step up.
But you must be the judge. At the end of the day, you're the king of the castle and the pack leader. You know your dogs and family and if he won't mesh, then that's also a valid decision.
My wife spends hours at the shelter before selecting a foster to bring in.
Sometimes they don't leave. lol.
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