To start off, welcome to Orchidboard!
A keiki needs to have roots in order to have any chance of living once it's been cut off. So for that rootless one, patience!
For the other two, how long is the root on each one. The usual recommendation is that the keiki is ready to be cut off once you have at least 3in of roots. Doesn't matter if it's 1 3in root or 3 1in roots.
How close are they to each other on the stem? if there is enough space between them to slide scissor blades between them (without risk of damaging them) then it's not a problem. To remove a keiki, some people prefer to twist them off the stem, but I'm one of the people who prefer to cut them off. In that case you simply cut the spike slightly above and then slightly under the keiki.
Could you post some photos of your keikis and plant?