I think you can forget "The Court"? This is highly lightly to be a bad transcription of "Y Llawnt" or "The Llawnt". In modern Welsh it should probably be written "Y Lawnt", with only one 'L', and there are lots of references to "Y Lawnt" throughout Wales today.
I think the most obvious translation would be "lawn" or "smooth hill" but place names can often be derived from not-so-obvious sources!
If you belive that Margaret came from Ruabon I would be worried! I wouldn't say that Ruabon was "close" to Llansilin though? Also, it would not fit in with any of the census data that you originally gave.
However, the village of Cefn, in the south of the old Ruabon parish on the banks of the River Dee, does include the districts of Cefn Mawr and Cefn Bychan, but I've not come across a Cefn Canol here?
("Cefn" = "Ridge"; "Mawr" = "Big"; "Bychan" = "Small"; "Canol" = "Middle")
I found the family at Cefn Canol in the censuses by searching for a "Robert Williams"; born "1823"; living in "Llansilin"