I am pretty sure the yud makes it לשון רבים so it would be "our masters, our teachers, and rebbes" all plural.
I am not sure why they would leave the yud in רבינו but take it out of the other two.
A quick search on Google found that some leave it out of רבנו and some keep it in.
I think moshiach will have to come though for us to understand dikduk.