Hi colly - I feel your pain to some extent, I am starting to go a bit stir crazy. I am home a lot at the moment as I am between roles at work.
Can you not shut puppy downstairs or at the bottom of the stairs behind a stair gate with a kong and take old boy upstairs with you to do housework up there? Similarly, in his crate and shut the door of that room and have old boy with you while you potter?
I have taken both dogs out in the car to my parents place and allowed puppy out on the patio in a lead, to change things up a bit and give us all a change of scene.
I do leave them both for up to an hour, one loose in the room, and puppy shut in his crate, both with a kong each, so I can go to the gym or swim. I also leave poppy in his crate with a kong to walk my older dog for up to 45 minutes.
I have two sons, 11 and 13 and as these are family dogs they do get told when they get home from school, that they are in charge and if there is a wee on the floor it is their fault for not letting the puppy out regularly enough. They have it slightly easier than you sound you do though as with the weather we have had since we got him we have been able to leave the door open and he does go out when he needs to. He is an 11 week black lab.
The boys will also he in charge this Saturday night and all day Sunday as my husband and are going out. They tend to do it in shifts, so one of them can play the PS4 for an hour upstairs and then they swap.