good advice above and the longer you wait to separate and remove any mirrors the harder it will be...separating is best when the birds are not only in a different cage from each other but a different room so they cant watch each other when you go to train and patience is everything with consistency to your rountine as well...like minimum twice a day for no more than 15mins and sometimes that will be less depending on the birds body languare as you dont want to try to rush them or force them by sort of chasing after them with your hand when they move away...

also offer the back of your hand in stead of a finger there is less to try to bite with using the back of your hand and more for them to feel comfortable with when they do go to step up...
get comfortable with these sessions yourself an speak slowly and softly as you will be teaching to talk at the same time if you say the same thing over n over like "STEP UP" be sure one person only does the training.