The word for 'sisters' is chwiorydd.
chwaer
her sister is Katie welsh
Mae dwy chwaer gyda hi.
'Mae gen y chi ddau chwaer'
In Irish it's "deirfiúracha" In Welsh it's "chwiorydd" In Scots Gaelic it's "peathraichean" In Manx: In Cornish: In Breton:
I know for a fact that people in Wales are called Welsh.
"You are Welsh" = Rwyt ti'n Gymreig
Daniel Owen, the Welsh novelist, had three siblings. He was the second of four children in his family. His siblings included one brother and two sisters.
Draig Gymreig
'gyda dy Gymraeg di' is 'with your Welsh'
The Welsh word for "Welsh" is Cymraeg :)
No in Welsh is dim.