New age tweens and getting them to be understanding

MAIN QUESTION: How do I get 2 pre teens to understand the necessities of education and taking care of their chores ?Hello all, I am the guardian of 2 young women (the oldest being a 12 year old female and the other being a 11 year old female) . And they have been under my care for the past month and I’ve noticed that they are lazy through out the day and don’t have a care in the world for most things. They also think of school as a time killer and not a building block to being successful so often times their grades are decent at best, but the thing that bothers me most school wise is their problem with authority. I can often over hear them talking about ugly and rude stories about their teachers, and how they got to them today.They treat me with respect most of the time but as soon as I ask them to do something (which is usually a small favor or a task that needs to get done for the next day) im public enemy number one. They are usually on their phones all day even when we are out, so I figured taking their phones away would be a decent way of getting them to listen to me. Which has the opposite effect lol, but after a few hours they do what I ask. I’ve also tried the task/reward method but these ladies think they are clever and ask for expensive items after doing something small. via /r/Parenting https://ift.tt/37W8Cjt