Hi C.,
I truly feel your frustration.
One thing I tried, and my friends have tried, and we find that it works, is showing the kids the consequences of their behavior.
Time-outs don't always work, so we get CREATIVE.
When my 2-year-old son colors all over, then the colors get taken away immediately with a brief explanation.
I do this everytime after, now he is gets it that if he doesn't
behave, it gets taken away for good.
My kids are usually fighting over some toy, so since they won't share, it gets taken away, and every other toy they fight over UNTIL they either have no toys or they start to share.
Sure, they throw tantrums, but the results have been well worth it! They understand that if they don't listen, they don't get their way.
Maybe you have tried this, but don't worry, YOU ARE NOT THE ONLY MOTHER STRUGGLING WITH THIS!
Take care and keep up the hard work,
R.