Merging Leasehold and Freehold

We've recently been granted probate of a property and are in the process of selling.

However an issue has arisen between the two conveyancing solicitors over the title deeds and we're not sure how to resolve it. The property (a residential property) has both a leasehold and a freehold title attached to it as they weren't merged when the original leaseholder bought the freehold a number of years ago. Both the titles were owned by the same person who we have inherited from.

The buyers solicitor is refusing to proceed with the purchase until the titles are merged by Land Registry, but our conveyancing solicitors are saying that this isn't necessary and the application will take too long and could be rejected by Land Registry anyway. The buyers are not applying for a mortgage so no lenders are involved in the transaction. It has got to the stage where the sale is in danger of collapsing because neither solicitor will budge from their stance.
I was basically looking for some advice on how long a merger is likely to take (we've been told there is possibly an option to expedite), whether there is a chance that it will be rejected (there are no obvious impediments to the merger, from a layman's perspective), and whether we can resolve the situation?

Thanks in advance 

Dan B - any application can be expedited if there's a genuine urgency. An application to merge relies on a number of factors, namely 

Merger can occur where a leasehold estate in land, together with the reversionary estate, come into the ownership of the same person and are held in the same capacity.

There must also be a clear intention to merge the estates.

Any mortgage on the leasehold title must be discharged.

The lease is absorbed by the reversionary estate and thus determined. For details of the various situations that may be encountered, the treatment of beneficial easements affecting the leasehold estate and how to make your applications against any affected titles, please see Determination: on merger.

You also need to take appropriate action in respect of the Points to consider on all applications, which sets out:

• what forms you should complete in respect of each affected title
• the documents you need to send
• how to act if either the lease being determined or its reversionary title are unregistered
• fees payable 
• how to deal with any incumbrances affecting the determined lease

So if the buyer won;t budge the ball is in your/your conveyancer's court as the seller. If they think it might be rejected the ley Q to ask is 'Why?'

Thanks for the quick response, much appreciated.

One issue that I forgot to mention in my original post is that the titles are not in our name as we are acting as executors. 

Dan - that maybe an issue but again only the conveyancers can decide. If he titles/tenures are not in identical ownership then that could be why they are taking issue with things and you may need to update the titles to mirror one another and merge the two before selling - but please do discuss with the conveyancers as it's something they need to decide/agree upon from here

Thank you