I'm in two minds as I can see it from both sides.
We own a home in Sydney that we currently have rented out as we are living interstate, where we rent. The house we had been living in (renting) in Perth was put on the market when we had 3-4 months left on our lease.
I hated the weekly open (and occasional mid week) inspections and would have given anything to break the lease & leave early rather than putting up with inspections, pest & building inspections, the new owners wanting another look, pre-settlement inspection etc etc etc. Our lease expired on 20 Jan which was such a hard time to look for a new rental (nothing came up prior to Xmas which meant that by early Jan, I had about 16 days to find a property, get accepted in a property (not easy with a dog!), pack, move and clean up the old rental. And all with an 12 month old and morning sickness with #2! It was absolutely horrid, but of course the owners wouldn't let us out early. God forbid that they should have been inconvenienced!! (yes, I'm bitter).
As a landlord though, I understand that you obviously don't want to lose rent.
Can I ask though, if they only have 7 weeks left on the lease, why couldn't you have put the property in the market then, rather than inconveniencing the tenant now?
In regards as to whether I'd let them break the lease, perhaps you can offer to split the difference (ie let them out as at x date). It probably won't work for them as they'll be up for double rent but at least you will have tried to meet them half way.