The dc have been at her's since Boxing Day and got back earlier today. They brought with them a card for me which had a letter inside it. Having read it I don't know what to make of it and would appreciate some opinions. Before I outline it, the backstory is ex and I separated in 2014 after he told me of his long term infidelity with a mutual friend. Divorce proceedings are now underway and custody is shared about 60/40 to me.
Mil begins the letter by outlining to me observations she has made of the dc's behaviour. They are 9 & 7 and she mentions how she ds2 winds up ds1 frequently, and says that ds1 needs help handling this. She then goes on to talk approvingly of ds1's love of a particular sport and comments negatively on ds2's craze on a particular age appropriate character, saying she hopes it will end soon as it is so shallow. This may explain her gift to them both of the charity goat things, if anyone saw that thread a couple of weeks ago. None of what she says is news to me, and I am obviously trying to deal with the issues as best I can, though I have no clue how ex feels about it all and they spend nearly as much time with him as me - probably more since I work longer hours and have to use childcare more than he does. She doesn't mention whether she raised these issues with him and, tbh, it reads like a massive criticism of my parenting.
She ends the letter by saying she is aware that I have not responded to her various attempts to stay in touch. She and sil have sent me vouchers for birthdays and Christmas since the split, though this Christmas have not done so, to my relief. I never knew how to respond and want no relationship with them. They've done nothing wrong (aside from being annoying in the way in-laws can be) but they are ex's family and I can't have a weird sort of relationship with them in which we never mention what an utter shit their son/brother is. Mil especially pissed me off at the time of the split by telling me how she has been on both sides of an affair and that ex 'would have been controlled by his hormones.' Yes, for 3 years I suppose 
. Anyway, he's her son, I get that, but I don't want anything to do with her after her comments. I think things will be even worse this year as the divorce progresses and ex seems like he is gearing up to fight me for more access to the dc and a mesher order. I can't possibly maintain some sort of bland relationship with them with all that going on.
But the letter is so long (she has form for strangely long and over-involved letters). Do I just ignore it? Or write back? In fairness she ends quite nicely by saying she hopes I'll go to her if I ever need help, but I do need to help now, but since the source of my problems is her son, it's hardly appropriate I go to her is it? WWYD?