Sorry you're absolutely right! And it looks like you are in luck, because there are quite a few surviving records from the Manor of Ewhurst.
I would advise you start by looking at the court rolls of 1440 and 1524-28 which are held (oddly by not uncommonly) not in the home county record office but in Essex Record Office. if you fancy a trip to Chelmsford, you should be able to order the documents in advance just by quoting the reference number D/DL M69 and the name "Manor of Ewhurst, Sussex"
There's a chance that your Crysford family members will be shown there - it may give you more information about dates when they took possession of property and what and where the property was.
After that you can trawl through the records in this series at the East Sussex Record Office - they look like they hold quite a lot of material from this manor all the way from 1326 to 1900. i wouldn't be surprised if you found various references to your family in these records, which might help to piece together some details of their lives and property through the centuries.