Thanks for your reply.
Well, the question you will first need to consider is whether you would like all of the 4 dwellings to be Leasehold? It appears to me that they will have to be- The 2 apartments certainly will have to be, and if the 3 and 4 bed dwellings share any main structure, they will have to be also.
On the basis that you do proceed on this basis, you will need to instruct an Architect to draw up some Land Registry compliant plans for each dwelling, showing the extent of the dwelling any any communal areas/rights of way. You will also need to instruct a Conveyancing Solicitor to draw up 4 Leases for each of the dwellings. The Leases will be on the same terms for each dwelling, and will details any rights of way and a provision that a service charge is paid in respect of the parking/joint access as well as for the upkeep of the main structure and any other communal areas.
You, as Freeholder, will then grant the Buyer of each dwelling this Lease, and you will initially retain the Freehold interest. As Landlord/Freeholder you will be entitled to charge a yearly ground rent if you wish and you will also be responsible fo rmaintaining the structure/communal parts, and claw back any expense from the 4 dwellings under the service charge. As and when the last dwelling is sold, you may feel that you do not wish this hassle and you could transfer the Freehold to the 4 dwelling owners.
If the 4 bed dwelling is totally separate to the other 3 dwellings, you could sell this as a Freehold property, with the other 3 remaining Leasehold. If so, you would need to still instruct an Architect to draw up a plan showing the extent of the dwelling, and as and when a Buyer is found, your Solicitor wouls just draw up a standard Freehold sale of part Contract.
There is of course a lot more detail your Solicitor will need to go through with you, but hope I have assisted and set out the legal position.