You will get stamp duty group relief (provided it is a group of companies) - provided you are not in the process of selling the properties (in a corporate wrapper).
Is company A going to sell the trade, or to be sold? (Obviously the final result is giong to be a factor of the desires of the purchaser.) But if it is the trade that is being sold without corporate wrapper, there's not need to bother with any of this.
What happens if the properties are transferred at MV and there is a large debt on the balance sheet on COmpany A when it comes to sell the trade?
It will have to be settled.
What happens if the properties are transferred at less than MV?
You may end up with the directors breaking the law. Depends on how and what - and I'm not going to comment on that, sorry.
Plan 2, to give you maximum flexibility. (N.B. effect on small companies rate with all the associated companies)
Incorporate E, F and G, all as subsidiaries of A. Transfer trade and properties to each of E, F and G. In the event of selling one of these companies within six years, interpose Newco between A and shareholders. Transfer E and F to Newco, then sell A and G together. No degrouping charge arises as you are selling A and G together.
Plan 3, which does most of what plan 2 does. Transfer properties to B from A. If you wish to sell the properties, interpose Newco between A and shareholders, hive up trade into newco, dispose of A and B with properties. If you wish to dispose of trade, move B up, and dispose of A.