I feel for you, The Perky Biscuit. Every weekend is a bit much. I presume, please correct me if I am wrong, that you only have one sitting room. If you had a decent sized kitchen diner in addition to the sitting room, another telly and a small sofa could go in there, or maybe a conservatory - even a spare bedroom but if you have, say, the average three bed house that won't work. As it is you are all on top of each other and if you're at work all week, you need time to yourself at the weekend, no matter how much you love your son and granddaughter.
These arrangements only work well long term in a big house where there is a lot of private space.
What I hope, for all your sakes, is that your son can get a place of his own before too long. I imagine he is working towards this, he must want it eventually. Can you help him with that?
In the meantime, he and his child need to go out for some of the weekend. You, too, can go out - and enjoy yourself, find somewhere nice to go, that interests you, maybe with a friend but also on your own, not too far away and not just going round shops.
I wish you all good luck - please see this as a temporary arrangement and make sure your son knows it, Then you can put a good face on while it lasts.