Boundaries

Hi, I have been unconsciously incompetent at holding boundaries with myself, my husband and my children. Through my new work in teaching a class of students am becoming aware & conscious of my incompetence in requiring listening and respect when I am talking.
I gather it’s from low self confidence (even though I think I project as very calm, positive, enthusiastic and confident). I am positive it also comes from low skills – I often find I can’t focus on things when others are around as I feel they have the right to interrupt me and ask questions and for help. I don’t seem to be able to say “no” firmly and kind – it ends up looking like me being mean and forceful to push through to the the end despite everyone demanding things from me and despising that I have to do something other than tend to their needs…and unless I am one on one with my children holding their attention for a meeting or worship is so so rare!
I would like to feel I have space for all I need to do and that everyone is happy for everyone else doing their own thing rather than being annoyed with the one person who asks for space to focus and is doing something away from them!

Open to all pointers!!