Lomaxes is the plural form. Lomax's is the singular possessive. Lomaxes' is the plural possessive.
You can also write say if your name is Suphil. Then you can write as Er. Suphil or even Eng.Suphil . Both are accepted.
"Write" is a verb, not a noun. Verbs in English mostly do not have singular and plural forms.
Write-offs
I can find no Welsh equivalent for the name "Claire'.
"Claire" is typically a girl's name.
Lomaxes is the plural form. Lomax's is the singular possessive. Lomaxes' is the plural possessive.
Claire Laing's birth name is Claire Heggie.
Claire Janaro's birth name is Claire Elaine.
Claire King's birth name is Claire Seed.
Claire Keim's birth name is Claire Lefebvre.
Claire Chevalier's birth name is Claire Ferullo.
Claire Trevor's birth name is Wemlinger, Claire.
Claire Tomalin's birth name is Claire Delavenay.
Claire Oelkers's birth name is Claire Oelkers.
Claire Patten's birth name is Claire Brisebois.
Claire Nielson's birth name is Claire Isbister.