Really the father could take on the daughter due to her more pacifistic nature and it would take the combined might of both the son and the daughter to take down abeloth and the father can still throw the son and the daughter around so he can provide some distraction and can resist there powers long enough for Abeloth to either take out one or save him.
Put the father in his prime he solos everyone.
Abeloth tanked the explosion of Sinkhole station, tanked canonfire from multiple GA blastboats, the explosion of Daala's hidden lab, an attack from Oneness Ben while amped by the Font of Power that could oneshot frigates, a prolonged attack from amped Vestara's lightning which could power ships iirc, tanked multiple telekinetic attacks from Luke/Krayt while weakened, iirc, Boba Fett's entire arsenal/multiple thermal detonators, etc. The son at best oneshot Ahsoka Tano while Abeloth destroyed Sinkhole station/sucked a darkside nexus and focused it onto a single point. She caused earthquakes on Coruscant, collapsed Friendship/the Justice Plaza, destroyed Tahv, knocked down 100s of Lost tribe Sith/Luke/Vestara/Ben with a TK wave, destroyed multiple Blastboats with a single force push, caused Earthquakes/a Volcanic explosion on Upkezar, and caused a massive Volcano kilometers tall that spouted tons of toxic ash killing scores of people on Coruscant. There is a lot I'm leaving out, she's just generally shown more raw power than either the Son or Daughter, more power in the force, and a wealth of force abilities they don't possess.
She's stopped lightning in its tracks multiple times, and has palmed it, and has the durability to suggest she can withstand his lightning
Originally posted by carthagewas she near sinkhole station when it blew? I thought she was on her planet
What has he done to suggest he can withstand an attack on the level of the one that blew up Sinkhole station? Assuming they're fighting on Mortis, she can probably just drain the energy of Mortis and do some serious damage