I have read about multi spawns with one male and one female and I was successful last spring/summer in that experiment and the result of that produced the breeders (1 male/2 females) that spawned in this 5g bucket experiment.
note-I changed my mind and will be leaving the male with his offspring
One thing I have noticed with leaving the male longer with his fry is that as adults they seem to be less aggressive. I feared that this would be a problem with spawning them and it has to a degree: Of the 6 males that I kept-one male ended up being a great spawner but an egg eater and I never got fry from him after multi attempts, two males would never spawn, just not interested, and 2 great- both with the females and eggs/fry and one that should have been culled but too cute so he is a pet never to be spawned or sold.
The one male that I could never get to spawn I used in this outside bucket experiment and he didn't have a choice but to spawn due to the aggressiveness of the two females, within minutes of placing the male in the bucket he was attacked by the two females and they demanded to spawn..or else and this stimulated him to want to spawn I believe, I wish I would have video of this, it blew me away, I have never in the over 10 years of working with this species seen this... after about 30 minutes eggs were everywhere, but these two girls had also been feeding on massive amount of free range live foods and fat as ticks in tannin filled rainwater.
Spawning with more than one female is a first for me and due to the success I am starting a new experiment that I will document later.
In my opinion or observation, I am successful with this in part because of how these Betta were spawned and reared-in a more natural method or as natural as you can get in a closed system, because this has never happened nor would I have attempted this with the Bettas I have spawned when I used a bare bottom method.
It works for me now- since I am retired and have lots of time....