A few more suggestions so Mom does not interfere with Dad's access to the kiddos. The not parking a car Dad buys is good, the liability in that is you would have to enter the child and that car on your insurance. Anyway, Television and computers are good to remove. If one of the kiddos doesn't like to read, require them to read a book and write a report on it to you before the grounding is over, this teaches them several things including writing and grammar, which children today seem to lose because of "text speak". A child who does not like to write have them write a short story.
One that does not like yard work, they do yard work in the way of mowing, pulling weeds out of Mom's flowers, cleaning up trash. Another is to volunteer for something like a soup kitchen. Mom needs to relax and start thinking outside of the box and spend less time thinking about how Dad is/could interfere with her parenting. In turn that will stop her from interfering with his parenting, because she will be busy thinking of creative punishments for unacceptable behavior.