Watching your son's lessons and taking lessons are a bit different, and if the girls behave it won't make too much difference to a teacher.
It very much depends on her personal attitude. If the teacher thinks that your kids are talented and are in need of extra lessons it's entirely possible that she'd love to help you out (and yes, in Russia it happens often enough).

In other words, if the teacher is ok with it you should not worry too much. You can give her a small gift at the end of the year to show your appreciation of her efforts if you wish (not money and not anything expensive, maybe a cake or a book).

But make sure first that she is willing to make adjustments and take your girls in, and it's not just Dmitry's delusions.