<p>The OP said that the mother is his wife’s sister, and his wife is the one who wants to support the nieces.</p>
<p>I say, OP, stay out of it! There is much more here than the nieces, the choice of school, etc. This issue is between your wife and her sister. You are in a no-win situation. Either your wife or your sister-in-law will be angry with you.</p>
<p>The only response you can have is to say to your wife, “Dear, I love you, and I will support wholeheartedly whatever you decide to do.” Then kiss her and go away!</p>
<p>There’s much more going on between sisters than meets the eye.</p>