Actually 3 SAE's, three female Endlers, male and female bettas, and some Tylomelania snails. The two bettas mated once but I think one or both must have eaten the bubble nest as it was gone the day after. I probably should have removed them from the tank after they mated. I understand that you're not supposed to leave them together but these two seem to do fine. The SAE's were removed from my 60 gal. cube because they had become too aggressive. They had started attacking other fish, specifically some swordtails. I'm surprised as SAE's aren't supposed to do that. I should probably have gone with just Otocinclus but I don't know if they're as good at removing algae as the Siamese Algae Eaters.
I'm going to add some male Endlers into the tank later today.
No jumpers yet but if they do our Miniature Schnauzer will be waiting to eat them. I caught her one day barking at one of my tanks right up next to the glass which spooked the fish. Sure enough one of the fish jumped out and she promptly ate it! Amazing how smart these dogs are. Now she either can't get to the tanks or they're covered.
Generally you remove the female after they mate, and leave the male with the eggs for 3 days until they all hatch. then remove him. I bred plakats before, and its difficult to take care of any fry in a non-breeding setup (because the fry shouldn't really be moved around and should stay in the tank they are born in until they grow up.) a Filter and gravel would not be good for fry, so personally i would not attempt to breed bettas in this tank, and would have done as you did (treat the tank as a regular community.)
I too left a pair of bettas in my 40 gal planted tank to try to see whether the female could consistently get away from the male via the dense vagitation offered in my tank, and live with a male. they did decently for a few months, there was some chasing but eventually the female disappeared so i assume she jumped out (open top tank like yours). I still have that male in the 40 (he is about 2.5 years old) and he is doing well on his own.
Aggressive SAEs is something I have seen because I started keeping them as a school of 5 tiny individuals in this same 40 gallon planted tank i was talking about. As they grew, they became more aggressive, but all aggression was contained withing their group. they did not touch other fish. Gradually i lost 2 of them so I have 3 left today (the first one was completely outcometed for food by the others, got stunted, and starved to death i think. the second one must have been chased out of the tank because he disappeared one day too.) As a trio they still contain their aggression withing their own group, not touching any other fish. These SAEs were raised in a planted community setting with fish like swordtails, a platy, mollies, oddly enough one goldfish (DOH), corydoras, otocinclus, and an angelfish throughout their lives in my tank. I do not believe they attacked any of those fish ever, except maybe taking small nips at the fins of the corydoras because both species occupy the same bottom tank level constantly.
All this leads up to my conclusion about SAEs - they do better in groups (I bet you started with a group too) and will contain their aggression within that group. possibly when their numbers fall down to 2-3 individuals, they might turn on other fish. The SAE is a peaceful fish only while its young and small. once they grow to a good size, they do become very...arrogant lol.
SAEs eat everything you feed to your tank, but they do take care of the algae as well. So as a group of around 5+ individuals, they can be a nice addition to a tank. That is what I think.
How large are your SAEs and for how long have you had these particular individuals? Perhaps you could get a school of them going in your 60 gal again. That should keep the aggression down.