Depends upon the current condition and reason for change.

I disagree with the advice above, the bathroom door that is in the passage should be closed. The reason for this is that you already have a bedroom without an attached bathroom. If you go by the advice above you will then have two bedrooms without an attached bathroom. Its not ideal. Also, you havent told us for which uses are the other two bedrooms. Are there going to be old parents in the bedroom with the bathroom or kids or are you going to use this as a guest bedroom? If you close the door in the passage you can have a bigger vanity by moving the WC behind the door that is from the bedroom side. This is also good because you should never have a bathroom door with a view of the WC. The WC is a very private spot and there shouldnt be a direct view of it from the room. Also we tend to spend more time sitting on the potty than washing hands, looking at ourselves or taking a bath. Once you move the WC you can have the vanity extending till the wall and will be 2.5x bigger than what you currently have.

Yes..which is why help is required (from professionals). I have the required labour, however would need help in the names of the products which are in use. Eg-Dr.Fixit vs lime (chuna).

Bathroom Renovation project at Sinhgad road Pune