Help with GSD's joint care

[14+kitties]

As some of you know we have a small cottage on our property which is occupied by a long time tenant. He has two GSDs. Logan, the daddy, has been suffering with joint pain for about two months now. He is 12 years+. I know the leg he is limping on has a huge lump on the joint. The tenant did take him to the vet a while back and he was given a shot which helped the pain for a few weeks.
Our tenant phoned yesterday and asked hubby if he could dig a hole as he plans to have Logan put down at the end of January. He can't afford to take him to the vet again as he lives on disability. We are not in the position to offer to take him either. It is tearing our tenant up thinking about losing Logan.
My question is.. would glucosamine help at all at this point? I have about half a bottle of glucosamine sulfate which I could give him to try if anyone thinks it would be helpful. If so how many pills a day. They are 500 mg. If it helped Logan I would continue to supply him with the pills.
Or am I just being stupid and at this point nothing will help Logan? :sad: