Is this right for 'i saw the man which is with the girl'
You have two tenses goin on at the same time...

"I SAW the man, who IS with the girl."

It really depends what you are getting at...

I saw the man, who was with the girl.
я увидел мужчину, который был с девочкой.

I saw the man, with whom was the girl.
я увидел мужчину, с которым была девочка.