I don't have any experience with autism. but....i wouldn't appreciate it if my mil(or my mom if she was still alive) would changed course on my child before my husband and i had decided to. things like bottles, potty training, pacifiers.. things like that, i think should be a parents responsibility.
my guess is she isn't very knowledgable about autism. just the little i know from knowing only a few aquantences with children with autism and reading on moms boards.. I WOULD EVEN KNOW NOT TO DO THIS.
yes you AND your husband need to sit down and talk to her. maybe not at dinner. but at a time with out the kids so it's not infront of them. be a united front. come prepared with printed information if needed. even if you have talked to her previously about what autism is and what sprectrum your son falls in.. i would bring PRINTED information. something she can read and not feel judgment.
i'm not saying y ou are going about prior conversations about this in the wrong way, sometimes we don't notice how WE are saying things either.. maybe preface the conversation with positives like we know you love our son with all your heart. we know you have raised a wonderful son(your husband) or other children. and that as much as you don't want your son to be different than other children, he is. and she needs to participate in you and your husbands parenting style. don't threaten that she won't get to see him. or anything like that. tell her by participating in the style that is needed for your son is only benefiting your son period.
and tell her as much as you know she was a great parent and did a great job with her children, if is now your husband and your time to do that same great job for your son. and you need her to be on the same page with them. for your son.
make it more about doing these things for him and not doing something for you and your husband.
if that doesn't seem to help , make a dr appt with your sons dr and have her some along for the sole purpose of the dr going over certain details about what your son needs directly to her.
goodluck. i'm feeling for you
we had to have a conversation with my inlaws a few weeks ago concerning things like not giving my 3 year old son rides on a riding lawn mower or letting a 6 year old cousin DRIVE the riding lawn mower with my 2 and 3 year old in the yard! (i about had a heart attack seeing this when we went to pick the kids up after staying with the inlaws for only the 2nd weekend ever..lol)they grew up on a farm so to them it's normal. my fil felt so bad and upset he called me a few days later and apologized saying how much they loved the kids etc. i felt sad too.. but i knew i had to stand firm on what i felt i could live with and letting my kids ride on lawn mowers wasn't one of them.
hang in there. not sure i was of much help
T.