Aneirin Hughes, who plays Ch Supt Brian Prosser, suffered facial injuries in the incident at a pub in Aberystwyth.
Dewi Lloyd Edwards, 24, received a community order and a £250 fine from town magistrates after admitting common assault and actual bodily harm.
Robert Meirion Edwards, 52, was fined £105 after admitting an assault charge.
The incident was over a long-standing dispute about agricultural land which has since been resolved, the court was told.
A third man, Steven Paul Welsby, 40, denied a charge of causing actual bodily harm.
His case was adjourned for trial next month. He has been released on conditional bail.
A father and son have been fined after admitting an assault on an actor from BBC Wales police drama Hinterland in Ceredigion.