Putting OEDD at the start of a sentence is a sign that the following verb is in the past tense. Is this correct??
yes, if the sentence is in the 3rd person (he was/she was/it was/the children were/Mr Jones was… etc).
Can you check me on the following please:
My brother wanted to = OEDD FY MRAWD YN MOYN I
Jack wanted to = OEDD JAC YN MOYN I
Yes, those are fine to say ‘your brother’ or ‘Jac’ wanted to do something
Diolch eto Siaron