Selling a house with a leased garage

Hi all,
This is my first time on here and I'm feeling a little desperate!
So a bit of background, we've been living at our current property for nearly 6 years, we have a garage attached to our house that has a coach house overtop, so it has a lease on the garage. We sold our house 7 months ago and there has been many issues throughout this time, at the start it was with us finding a new property, our buyer has been incredibly patient and has stuck with us all this time, he's a first time buyer and has this week told us we've got 2 weeks, if he isn't moving in in 2 weeks time then he is pulling out, frankly I can't blame him because it has really dragged for him.
So baring in mind our solicitors have had since February to sort out the selling side of the property, they did very little at their sort of own admission, until we had found a property to buy at the end of June. They've known all along about the lease but have really dragged their heels. The lease is £1 a year, we've never been asked for the money and the people who owned the property before us had also never been asked for it, so it feels as if it's slowing us down over nothing. Solicitors have sent a questionnaire to the owner of the coach house who is also the owner of the lease about 2 weeks ago, he only needs to fill this out, send it back and that's it, we can kick on with the exchanging.
My concern is I've heard about this guy and seen him a few times (he rents the coach house out so is rarely here, we've seen him for the first time about 3 months ago) and he doesn't come across as someone in much of a rush to help others, I may be getting him completely wrong but that's just how he comes across. Our estate agents are phoning him everyday as his house is rented through them too and he doesn't pick up or answer. He lives in a caravan according to his brother who we're friendly with and gets his post delivered elsewhere.
Sorry for rambling but basically I'm concerned he is going to ignore the letters and calls and it's going to cost us this sale, is there anything we can do? We've asked if we really need this questionnaire to complete and have been told we do, but I really don't think this guy is going to ever reply.
If anyone has any tips or have had a similar issue I would be so grateful to hear. Thanks so much!!