Ken Dickie, 64, died after the incident at the Rockley Park, Poole, in May.
Jamie Mitchell, 35, who was cleared of a manslaughter at an earlier trial, had admitted common assault.
His mother Samantha, 57, received a suspended sentence after admitting attempting to pervert the course of justice.
Mitchell's trial for manslaughter in January heard his mother and Mr Dickie had been in a relationship for several years and were going through a "down phase" when Mitchell visited his mother at the park on 7 May.
In the evening, Mitchell accompanied his mother and Mr Dickie to the holiday park bar and got "tanked up" on alcohol.
The two men had a confrontation outside and were separated by members of the public.
The court heard the pair had initially told police that Mr Dickie had pushed Samantha Mitchell and she had pushed him back.
But Mitchell later told police that he had tried to push the couple apart, causing what he described as a "tragic accident".
At a hearing at Winchester Crown Court, Mitchell, of Apple Close, Poole, was sentenced to 10 months and four weeks imprisonment, suspended for 18 months, for common assault and perverting the course of justice.
Samantha Mitchell, also of Apple Close, received nine months imprisonment, suspended for 18 months, for attempting to pervert the course of justice.
A man has received a suspended sentence following the death of his mother's partner who fell and hit his head at a Dorset holiday park.