purplegoats you are human, humans sometimes shout. Relax, it is OK.
Lots of good advice already.
I shout a lot! Far too much.
I'm not proud of it but this is real life.
How long have your girls been with you and are you adopting alone?
Push for more support if you need it.
Totally agree on calling it ''indoor voice' and perhaps 'outdoor voice'. I might make a joke, (as long as they will not get upset), 'Hey, I can hear you fine, I'm not on the moon!" etc. (Yes, not very funny, but add a few silly voices and smiles and you can defuse situations sometimes).
Try and have few rules, if you can. Make sure sanctions are relatively small. Once you have lost tablet or TV for the whole day or, goodness me, all week, what is there left to live for! (Or computer time or whatever.)
Losing a privilege for even a few minutes can be as useful a 'punishment' as taking it away all day.
Use 'Calm down' times or 'Take a break' which are not a punishment but work to relax the child and kind of re-set. You can go through the pattern when they are calm and use a teddy or dolly to be the child.
Prepare a call down or take a break spot. This can be a big cushion or bean bag on the floor in the room you are in or could be a chair/stool or step, and could be elsewhere but ideally within sight of you.
Be careful, this is not the naughty step, and some children will react badly to being put out of the room you are in. A cushion or mat is ideal as very portable. Try and keep it in the same room, or if out of the room, within eye sight. This may work with children of any age but adapt for the age.
So, back to the role play, if Teddy is not behaving appropriately, Teddy gets a warning (tell the child what you might say but let the child give the warning... eg... 'Teddy, please play nicely with dolly! If you don't play nicely, you will need to have a calm down time or a take a break, etc).
When teddy proves utterly unable to behave have your child put teddy on the calm down spot. Calm down time would only be about two minutes and ends with Teddy re-joining the fun with no further comment.
No need to apologize, because this can reignite the issue. The aim is for Teddy to forget the problems that caused the issues and move on.
Of course if the behaviour involves biting or hurting another person (or themselves) you will need to address that once all is calm.
Never leave in calm down spot for more than about two minutes. Always give a warning. I was introduced to this as 'Take a break'. Call it what you will but not naughty step or naughty spot.