Two brothers competing to see who can sleep with their mother first.

[runnerups]

A story about a bet between two brothers to see who can bed their mother first. Would follow the POV of one of the brothers and with slow tension filled group events where they slowly whittle down her reluctance(introducing nudism/yoga/massage) involving the mother occasionally stoking jealousy in them by showing unpredictable favoritism.

 

[John_Vandermeer]

You could up the competition by introducing some D/s in it, whoever has the upper hand persuading the mother to "punish" the loser, raising the stakes further.

 

[OnlyHappyEndings]

You might like this one:
https://www.literotica.com/s/rita-puts-family-first

 

[Carnevil9]

Although it's not an incest story, I always thought a good plot would be two friends (not brothers, but best buddies) competing to seduce each other's mother.