I too would be concerned that therapy might pathologize developmentally normal behaviors.

I smiled when I read your description of your children because developmentally, the challenges they're each facing (whining, temper, "sass" ) sound age-normal. It's really about teaching at each stage how to recognize and meet needs for things like self-advocacy, impulse control, independence in more appropriate ways.

Focusing on teaching and developing those coping skills in their natural environments, which for kids their ages are home and school, is likely going to serve them best in the long run. It might be more effective for you to have a conversation with a children's therapist or parenting support person to learn how to best foster healthy development and what to watch for, so that you can continue to help the kids learn and thrive.