Re: The Role of Sempai
Hmmm..... it is a fine line to walk. Hopefully they have enough experience to realize that grievous injury can result if someone doesn't have the ukemi to receive a technique. And the insight to realize that everyone has their own learning curve.
However, from the sound of your post it seems like they want to bull their way through class with a 'survival of the fittest' mindset. I think that since the situation is alarming enough for you to seek advice here, then it definitely warrants a conversation with the individuals, off the mat of course. That is your role (with deference to Sensei). Their role is to actually listen.
So, do they injure people? (more often than the odd training injury)
What does your Sensei think, and how is he/she dealing with the situation?