Just carefull there, as far as I know about SH they'll get aggressive towards same species(usually there will be the strongest one will bully the others)/other species, but thats all depends by the individuals.
I've experienced that before, that time I was giving that guy?(which still at 3") a saddled bichir (endlicheri) size 4" as tank mate, but in the morning I found that endli beaten up and dying
, fortunately I move endli at quarantine tank and giving lots of care so endli saved from death and still healthy till now.
Also.... I'd like to remind you that if 2 of them getting paired, I suggest you move the other fishes to another tank and leave the tank only that pair (since the agression will be maxed out).
I'll also want to share a bit about my SH diets (I also did same with my other predator fishes), I feed my them with MW, frozen shrimp, Night Crawlers, Crickets (with a rotating schedule) . I also gutload them with leftover veggies (cucumber, lettuce, peas, etc) and sometimes spirulina powders before i feed it to my fishes for their nutrition needs and color boost.
Good Luck Mate!