How to handle child tantrums?

My daughter’s are 7 and soon to be 6. Their dad and I have been separated for almost 2 years and he is married now. They have been through a lot. Between him taking them hours away and refusing to give them back to me for almost a month and there was a period of time I spent in jail. Before that I had never spent more then 24 hours away from either of them. We we’re always together. My oldest has had behavioral issues for quite awhile and has been in conseling. My youngest has been the easy one through all of this up until about 2 months ago. Now she’s acting out also. I’m at a loss of what to do. They have been on a schedule with their dad and I for about a year so they have a routine. But their behavior is so bad. I feel like I’ve lost complete control. They dont listen to me whatsoever, they talk back, and are completely disrespectful. These were once amazing behaved children. The other morning they were late for school because they both kept running from me and locking themselves in rooms. I’d get ahold of one and the other would take off. Went on for 25 minutes before I lost it and just screamed at them. Finally get them in the car and my youngest asked to have my phone. Of course the answer was no after all of that. She’s not used to being told no either. So she opened up her orange juice and dumped it on me. My oldest was even in shock she did it. I was so frustrated and at a loss at this point I just started crying. At this point I know she started she feel bad about. I just dont know what to do anymore. I don’t think they act like this at their dad’s but I know they are having problems with them as well. I just don’t think it’s as bad. I have tried time outs, im not big on spankings but after so many times I’ve even tried that. Spankings dont face my oldest. With my youngest it hurts her feelings if I smack her butt. But they still go right back to it. Because they go back and forth between their dad and I it seems as soon as I start getting somewhere with them they have to leave and I start all over when I get them. We we’re at the mall and I was up paying for all of their stuff and the two of them started running around the store screaming and throwing clothes. I was so embarrassed. I don’t know what to do. I’ve lost all control. Any advice would be appreciated?!