Hi dear client,
I've been working hard on your project.
As you asked, the main idea is to add three bedrooms and a bathroom to the house and rethinking the division between the living room and the family room.
In my opinion, the element that will divide the family room from the living needs to contain the fireplace and also a TV for the living and a bookcase for the family room. You can see the proposal on the rendered images. It keeps the two spaces divided but they still have some visual connection. Also the style proposed for the two areas is similar.
The living is more formal and the family room is the casual one. In the old fireplace hole I think that can be great to have a little working station. You also have a complete home office room in the night area but this little computer space in the family room that can be hidden by the wood panel can be a nice place for light working being surrounded by your family.
In the night area, I have designed all the kids bedrooms to fit the same: a large wardrobe, a desk and a double bed. You can try if it's better a double bed or single one and also the style of the bedrooms.
The existent bathrooms stay as they are (I have drawn them different because I don't know the actual disposition of pieces, but they stay the same) The new bathroom has a shower like you mentioned.
The main bedroom area has now a walk-in-closet with a bench that can be closed with sliding panels. Also there's a relaxing area with two armchairs for reading or maybe just chatting.
Hope you like it as much as I do.