Robert CRUST of Aldington m Charlotte COBB of Aldington at Aldington by banns 4 Jan1823 - witnesses Phoebe CRUST and Charles LUKEHURST - would Phoebe be Robert's sister?
Have you followed all these CRUSTs born/baptised in Ruckinge through all the census to see if there are any clues there ie. a brother might be living with a sister etc.?
And through the parish registers ie. Phoebe CRUST married Thomas DRAY at Ruckinge 1824 (mid Kent marriage index) etc. etc.?
I would suggest that's the easiest next step .......... just double check everthing about all of them.
Casalguidi 
Thanks again.
I think Phoebe is Robert's sister. Charlotte (COBB)'s son John is baptised the same day as Robert and Charlotte are married. Robert CRUST is direct to me, so I knew about the marriage, but had missed the baptism previously. Charlotte was buried 20 Dec 1824 in Aldington, I don't know what became of son John.
Phebe (sic) DRAY is on the 1841 census with Thomas DRAY, (son) William (age eight) and (brother) Thomas CRUST (age 50), all in East Ashford (I haven't seen the image / transcript, only advanced search at FindMyPast). I can find Thomas CRUST on the 1851 and 1861 census, but can't view the images as my credits at FindMyPast have expired

I think Thomas CRUST died Q2 1869 East Ashford, age 84.
From Lis's notes, a marriage:
William Ward & Mary Crust 11 12 1813 he of Sellindge
and a baptism of their son:
Henry bap 30 Apr 1814, Ruckinge
but no luck finding them on the census.