OP--I have read through all the posts and did not see what I would do suggested, so here goes:
First, I would not ever bring the topic up to the DiLs (or anymore to your sons--though I think you handled that excellently

). I would only respond if they bring it up again (and I would probably fail to notice any emails about it).
Secondly, when it does come up I would respnd with polite and kind bewilderment. It is, after all, totally bewildering. So, if she says she does not think you should go to Disney all the time, just ask her in the nicest, most confused and sincere wanting to know her answers way possible "Why does where I vacation matter to you?" If she says she thinks you shouldn't go to high school games say "I don't understand why it is a probelm if I do things I enjoy. Am I unintentionally hurting someone by being at the games?" If she says your DD should not spend so much time at home say "Did Sarah ask you to talk to me about something? Do you know of or suspect Sarah is in harms way or could be likely to harm herself or others? Oh, then what is the problem with Sarah?
Truly, if I were you, in addition to being hurt and saddened now--I would be confused as heck and I would really, and truly want to know if DD had valid answers to those questions. If she really wants to take a family vacation with everyone to Hawaii but feels she can't because you always go to WDW or something--perhaps she will tell you (that is a strech, but what I am saying is you DO want to know how this concerns her so you can be genuine in asking and not mean or harsh). If it turns out (as it likely will) that none of this really concerns her-- she pretty much has to admit it and should eitehr eventually drop it and move on or she may turn out to be not the sweet girl you have believed up until now (hopefully it is the latter).
Of course you spend more time with Sarah than your grandkids. Sarah is your CHILD whom you are RAISING. It would be horribly unfair to Sarah if you tried to treat her (your daughter) as only an equal claim on your time as your grandchildren.
As far as babysittng, I do suspect the Daughters in law are hoping for more. They are darned lucky you babysit at all. It is not your job to do so. Grandparents should develop relationships with their grandchildren when possible--but that does not need to invovle any babysitting. Do not feel guilty about that. I wonder how your DiLs would react if you suggested that you would like to spend some "adult" time with them and your sons and asked them to hire a babysitter so you can all go out to a kid free meal?