To me it sounds like you need 3 things...
1 - A much faster lens for low light indoor work
2 - A wider angle lens to allow you to fit more in your shots
3 - A proper flash
My lens suggestions would be the Nikon 35mm f/1.8 which would be excellent for your low light work as it'll give you nearly 2 stops more light than the 35-70 and the Sigma 10-20mm for a wide angle.
As for a flash, something like the
Nissin Di622 might be a good starting place. It's got full i-TTL compatibility so it can work automatically like the Nikon own ones but it's only £100.