Its Mam-gu and its pronounced "mam (as in lamb) gee"
Nain (pronounced 'nine') is the north Welsh name for 'grandmother'.
Grandmother is mam-gu in the south and nain in the north.
"Kigh"
seanmhair or seanag
an-"eye"-rin
es-i-th-t
The welsh name Rheon is typically pronounced as "HREE-on". The "H" sound in Welsh is pronounced with a rough, breathy quality.
I cannot find any evidence that is a Welsh male name.
The Welsh term for 'great grandmother' is "nain fawr".
Ceri is pronounced like 'kerry'.
I believe it is said TALLY-ESS-IN. It was the name of an ancient Welsh Poet, it meant Shining Brow in old Welsh.
Siôn is the Welsh form of John, and is pronounced SHON.