Dear MIL-
Even though you live in another country, you still have 6 grandchildren in this world that you should love, care about, and acknowledge. You should know their birthdays and send a card at the very least. It would be nice if you sent cards or small gifts for holidays and milestone events such as bar mitzvahs and graduations. In this day and age of computers and social media, there is no reason why you can't reach out and stay in touch with your grandchildren despite how you may feel about your son or myself.
Your once-a-year token call asking if you dear son is CEO of his company yet (he isn't and wont be), whether child x has gotten in to Harvard (he didn't nor did he attempt to), whether we've built an addition onto our too-small-for-you house (want to fund it?), and whether we'll be relocating to your country (not planning on it!) is mean-spirited and hurtful.