Can you communicate with people in your dreams?

Yes, you communicate with your own subconscious mind - not with other people. That is actually what dreams are. They're your subconscious trying to communicate with you.

When we're awake, there is a barrier between our conscious mind and our subconscious. When we're asleep, this barrier relaxes and our subconscious thoughts, beliefs, feelings, hopes and dreams, and whatever about us and our lives that aren't dealt with while awake come to sort themselves out. This is hard for us to recognize because dreams are representational. A tree could be your mother trying to shelter you from something, a dog could be your goals or ambition in life that you're not taking proper care of, etc. Our dreams are our reminders that we have unfinished business that needs tending to.

Not with people other than one's self. There is no magical transmitter/receiver in the human brain that picks up signals from other brains without using the eyes or ears. To communicate with other people who are not physically present, humans need to use technical devices like cell phones and the internet.