HI OP, you've posted in Higher Ed (ie University), which is probably why you've had no response.
If you post in Secondary you may have more luck.
(btw my son went to Grammar, but in Bucks, and feeder schools are not relevant here, they just have to pass the 11 plus. My son didn't have a tutor but did some practice papers for several months before the 11 plus to get used to the sort of questions.
Your SIL will find tons of advice and local info on the forum "11plus"