I'm so sorry for your loss.
I agree with Mercedes--would it be at all possible to keep both dogs? They've already lost their beloved Dad/your Grandpa, and then to now be seperated from eachother too, would only be that much harder on them. Tooker looks so sad, bless his sweet heart.
It's your decision though, of course. Again, I am so very sorry. May your special memories of your Grandfather bring you comfort during this difficult time.