Setting boundaries

Annie 🇬🇧

I'm due to have my first child in April. He'll be the first grand child too.

I find it hard saying no in general, which worries me in the future when my baby is here.

Don't know why I feel bad after saying no, I know I need to change this for my child, mom guilt would probably be worse.

Im currently living with my in-laws.

How do I set the boundaries without sounding rude or harsh?