I think we can all see the problem, Sandy, honestly.
You can only go out with the big dogs in the late afternoons, evenings or weekends when Steve is home and you'd prefer to take all three with you. But I think we can all see the funny side of it so much more.
I'm sure no-one means to offend though
There is a solution though. You and I can take the pups out for a lead walk in the daytime - just them and us, they only need about 15 minutes a day, perhaps less if they get tired in the first couple of months. And Rohan can be in the dog room with Ben and Islay during the day, with access to the bottom section of your garden or further up when you are with them. Then the pups can sleep for an hour - perhaps with their tea with them, while you and Steve, and perhaps me, go for longer walks with the adult dogs! That is plenty of exercise for her till she is about six months.
If you used the push chair idea it would be too tempting just to let the pup out, and it
does do untold harm to young limbs and bones to over exercise. Bobby is allowed to run in the front garden (half an acre) for five minutes at a time, possibly three or four times a day, and that will be the same till he is at least 6 months. And some of that time is training to recall, sits, stays and retrieving, introduction to the ducks and chickens. Then he is taken in and put in his pen to sleep. He gets out a few times during the day to play with his Mum and Uncle, so is getting plenty of exercise.
But in the end of the day it's up to you. I WAS joking too - I
would come with you if you decide on the pushchair