Can plaintiff have some witnesses as defendant

I cannot answer your question without knowing what court you are in, and what proceeding (motion, trial) you are preparing to handle.

It is not only possible, it is common for at least some of the parties' witnesses to be the same.  When providing a witness list, you neer want to leave anyone out just in case; if you leave someone off the list and later need them to testify, you may be precluded.  BTW, it is very  unlikely that the affidavits your witnesses provided will be admissible; they will have to testify, in court, under oath and subject to cross-examination, not provide affidavits.  Generally, the way you get "sworn statements" from opposing witnesses before trial is by deposing them, but it may be too late for that now.