Hello,
I have read through your requirements.
I have a ready made solution to be deployed for realtime chat, with complete backend on NodeJS and Mongo DB using sockets, and android application with chatting module integrated.
If you require this module integration in your app, it can be done also.
Get in touch with me to get the task done quickly and effectively.
I would really love to help you out on this.
Thanks
Naveed Ahmed