Here are some training examples that I deal with in class daily :ukes trying to spin out of shionage in turn I go into kotegaeshi second turning there body out of ikkyo transferring into sankyo or yonkyo and lastly trying to put on nikkyo and before I can apply it there tapping out and the instructor sees this and tells me not to transfer into another technique and he demonstrates on them they try to spin out he takes them down to the Matt but when I do I,m being to rough WTH.
I take it that this is what happens mostly with the lower ranks. Then either a) your technique is incorrect and is causing them to spin out and you need to slow down and focus on getting that right or b) they don't understand how to take the ukemi yet and that is up to sensei to teach and you are only confusing them more by changing techniques.
And if they are taping out early in nikkyo then you are probably causing them pain without actually correctly or effectively applying the technique. And again this means you need to slow down and work on correct form.
And I say all of this because I have experienced the same problems you are describing and these have been the solutions/answers to them in my case. In other words the problem is not your training partners the problem is you and you really are being too rough. Sucks don't it?