Bore da
A few things have gone wrong here and in other changes you have made.

The name Bwlchteulu applies to the farmyard, not a single building. You should draw the farmyard and add the name / name:cy to that.

ruins is not a top level tag
You should use historic:ruins <whatever it was> or building=ruins.

ruins=Ynys makes no sense, probably should be building=ruins name/name:cy=Ynys

Diolch Phil