回复：我是个极糟糕的妈妈！诚心向有两个孩子的妈妈学习！

You 2 kids' reactions are very normal after be raised by other people than than parents. It must be so terrifying for them by taking away from their beloved people who raised them and moved to a strange world. It is time for the parents to recover their lost feelings, but it is a lot work. As parents, you need to understand why they don't get along with each other. Obviously, after your younger daughter returned back from China, you must treated her extremely well due to your gilt and you probably don't pay as much as attention to your old one as before.your older daughter saw all that and of course for a 6 years old who wouldn't understand why this little girl all the sudden showed up in her house, became her little sister, now taking her mommy away. From kid's view, that is horrifying, so she blamed on your younger daughter. There's might be books for parents who are in this same situation, kids stories in this kind subject matter to read to them. Possibly, you can seek for child psychiatrist‘s help. If you have trouble finding source to help you, ask your kids teacher, even your local librarians for book information.
Best luck to you and your kids!