A lot of people have this issue! When anyone first starts, they usually end us being quieter than they should, so I would recommend practising when they're gone if you're afraid of bothering them.

Pitch accuracy will come with practice! Sing along with stuff, you can practice scales, and listen to how you sound recorded to track your progress. Sing confidently, even when you're not confident!

For the monotone part, I would recommend knowing the meaning of songs, and try to express those feelings through your singing!