what is the answer for this question? is "karibuni" right?
Karibuni would be for more than one person. In this case you'd say karibu.
Much as I deplore the dumbing down of English, it is a fact that "Can I....?" is now an acceptable alternative in English to "May I...?", unfortunately to the point that even I use them equally <shame-face>
The dumbing down of English began when we stopped marking gender and case on our articles ...
"May i come in mama?"... is wrong?
'may I enter', or 'may I enter in' should be acceptable
"May I enter," or "May I enter in" are common English phrases and should be acceptable