[xpto123]

I think if you are not under a visa you should just find another job, give an excuse, server your notice period and leave without much fuss.

AFIK there are thousands of other jobs out there waiting to be filled, so why would you accept those conditions?

Telling the others that they are being grossly underpaid directly while leaving might make you be seen as a troublemaker.

But if your colleagues ask your new salary which they likely will, you can just say the truth and they will get to the same conclusion (but pass on this info closer to the exit date).

This way you would basically get a better job and tip your colleagues while staying honest, acting professionally and doing nothing against your conscience.

You never know, they might actually know that they are being underpaid, but they like the job, its 10 times what they make in their origin country already and they want to keep the visa at all costs.