The only way I got mine to eat when I brought them home was to feed some live adult brine shrimp, as the baby brine were too small for them. I'd get them started on live brine, and then wean them to what you have after they are used to eating what you put in the tank. Which may be 4-7 days.
Once they are eating feed some frozen bloodworms also, because shrimp are not terribly nutritious for them, though they are good to alternate with. They'll need live baby snails for their teeth as well.
The oto may or may not do well in there with them, so watch him carefully. These are unbelievably vicious once they decide they are going to go after something, but I've kept them with dwarf plecos without trouble so hopefully it'll be okay.
Good luck with your little fellows - I love 'em!