I haven’t read any other replies, so sorry if repeating. I’d decided ‘ no’, from your third line, just leaving him overnight. Once I got to the dog...and then your MIL taking it personally.....forget it. He is the most precious thing in your life, there’s absolutely no need for overnight stays at his age. If anything happens to him, to most people it’ll just be something horrible that happened, and will become a distant memory, but you’ll live with it forever. Don’t do it.
Last letters become first - March 26
Survey on British Women's Perspectives on Politics and Social Issues


so that they can re-establish their relationship with their DGS.