no your summary is correct - the 1780/1790 mixup was my typo in 1st message - the son predeceased the father

key to much of this are the wills - look at MNNB - remember the strange feature by which Douglas was in the ecclesiastical parish of Braddan (all wills pre 1880 went thru church courts) but in civil parish of onchan(property deeds + census)
I went for a douglas based fam as the marr of thos putative parents had no indication of out of parish spouses