I think the rule of thumb is that you should have about 3" of root on each keiki before potting it up. That can be 3 1" roots or 1 3" root or any other combination.
You should be able to gently twist them off. I don't know this orchid but on my kingianum they came away with a simple twist and then I potted them up.
agree with Rosie - the few keikis I have removed twisted off fairly easily - and I have read the same advice regarding the amount of roots they should have before being removed