Cdn, I understand your concerns. But as a couple of posters have mentioned, DS has only been back a few days. He DID message you and might not have thought your response required another immediate response from him. As BlueBelle says, there's no reason to message him that he can call you when he's ready. He knows that and, no doubt, will see your new message as an another attempt to elicit a reply from him. IMO, you need to back off.
It's possible he's angry that asked him to pay for his food if he stays w/ you and DH. That may be why he chose to stay w/ your X instead. Perhaps X didn't ask him for anything... sigh... It's also possible he's mad you're refusing to cosign the mortgage, and he's hoping he can get X to do it.
Or maybe he's just busy getting settled in. If he were angry, why would he even tell you he's here? You know him well, but maybe can't see the forest for the trees? I think you may be reading into what is only a few days' silence.
I get your concern about possibly being distanced from your GC. But I agree w/ those who say you and DH must protect yourselves. Please don't be talked/guilted into co-signing. You know where that will lead. Besides, he and DIL really need to learn to work things out by themselves.
For now, please be patient and encourage DH to be patient, too. Wait for DS to reach out to you. If he asks for money, just let him know, you're sorry, but you just don't have it to give anymore. Accept his new found relationship w/ his dad (even if it's just about money). Continue, for now, to hold out hope that you'll see the GC when they're in Canada. Best of luck!