Siemens Step 7 Queue Systems

I have done queue systems before on SLC's but for some reason i am really struggling doing the same in siemens step 7. What i am trying to do is the following:

I have 4 lets say "Instruments":
No.1
No.2
No.3
No.4

And also i have the following "queue positions":
Position No.1
Position No.2
Position No.3
Position No.4

When any of the instruments commanded to do a certain "operation", i would like to move it into a queue position e.g
If Instrument No.4 asked to do an operation before any other instrument, then i want to move Instrument No.4 into the Position No.1. If then Instrument No.2 asked to do the same operation then i want to move Instrument No.2 into the position No.2 etc
In the end my queue should look like this,lets say:

Position No.1 "Instrument No.4"
Position No.2 "Instrument No.2"
Position No.3 "Instrument No.1"
Position No.4 "Instrument No.3"

According to the above queue system "Instrument No.4" is operating, but the rest of the Instruments waiting into the queue until "Instrument No.4" finish its "operation"

When "Instrument No.4" finishes its operation, i would like to remove it from the queue and shift the rest of the instruments one position up. The queue then should look like this:
Position No.1 "Instrument No.2"
Position No.2 "Instrument No.1"
Position No.3 "Instrument No.3"
Position No.4 <empty>

Hope the above gives an idea what i am trying to do. Hope someone could provide me with any suggestions. Sorry for the length of the text. By the way, i am not the most experience PLC engineer in the world. If you would like any more explanations, i am more than happy to provide it to you. Thanks for your help in advance.

Here's some ladder that might assist: