I do think you need to work on remaining calm. You DO have more strategies than you think, you CAN be in control. I feel for you as you sound so tortured by how you are with them when you lose control - it would be so nice for you to have peace of mind that you are not doing that to them, or to yourself
I do know how frustrating it can be. With my 7 yo ds I think routine is key - in the mornings we have the TV on after breakfast and he knows that as soon as a certian programme comes on, that's getting dressed time. And when the next one comes on, it's time to be out of the house. By the way, I still help him dress. So shoot me! He needs organising and helping, he is immature for 7 and I'm frankly not worried about it - he won't still be asking me when he's 16 so it's not an issue for me.
You say you have no real issues with them - so I would just physically help them more and not worry about it personally. Lay everything out the night before so you're not chasing round like a headless chicken, then just help them dress and do teeth
You won't be creating the old 'rod for your own back' chestnut because imo children's own internal impetus for independence kicks in and they naturally want to do stuff for themselves at some stage.
Agree with ensuring they are looking at you when you talk to them, don't talk from another room or the other side of the room - be in their faces, politely! Also agree with lowering your voice instead of shouting. Perhaps you could try a star system for dressing/doing teeth/or whatever, and they get 50 per star or something to spend on Saturday for each task they do on their own?
Basically you just need strategies in your back pocket, because knowing you have somewhere to go other than just screaming out your requests, keeps you calmer imo.