Hi Keith
As far as I know, the letters on this site's database are the same as the originals held at the Beinecke Library at Yale, scanned by Andrew Birkin after he received them from Nico Llewelyn Davies and before they were sold at auction to Yale.
Andrew himself might be able to decipher them, as he quotes passages from the letters in his book of The Lost Boys. Are there any particular letters that you find difficult, that perhaps we can help you with?