As a teacher in a school for children with mental health challenges, I see a lot of variations of behaviors you describe. Sometimes, hard-core ongoing defiance signals a lack of trust due to trauma/loss/ emotional instability. Or it may signal Autism, a processing disorder, depression, or another problem. All of these things are helped by having a simple routine. Keeping the environment streamlined is also helpful as too much stuff/ stimulation can be overwhelming. Exercise/dance/music or any other patterned movement is very helpful. I encourage you to try to get intensive in home therapy and also to give your children a high quality chewable probiotic ( talk to doctor first and make sure the probiotic is GNP certified). Also, play Sesame Street or Disney songs with lyrics on the screen (just search YouTube for the song title “with subs”). Singing this way is good reading practice, and will bring you closer as you have fun and do something together. Almost as importantly, singing soothes the vagus nerve and tells our bodies to relax. Good luck, and do get some support!