Managed to get to the Museum briefly today and had a look at the Deeds you mentioned. Isable Kewley widow of William Kewley signed over a parcel of land at Kerrow Dhoo Onchan to her second son Stephen, who had married Catharine Skillicorn and was living in Lonan at the time she signed the land over to him which also ties in with my lot as the 2 eldest sons were born in Lonan and the rest of their children were born / baptised in Onchan.
I couldn't see any other transactions on the SSS or the mortgage to pass the land from Stephen or Catharine Kewley to Philip which would have made me very happy but I'll have to dip my toes into the Lib Vas etc and see if that helps.
I did find Isabel's Will 1769 which hadn't been filmed by LDS but it told me nothing at all other than she left her goods to her daughter Alice.