Sorry you are going through this OP. I'm one month off my wedding (been planning wedding for 5 months) and we have had very similar problems to you with both our mothers.
We asked them at the beginning of the planning process if they wanted to let us know if they wanted anything in particular and both sets of parents said they just wanted us to have the wedding we wanted and they were too busy to help.
Roll forward two months and both sets of mothers had taken their crazy pills. I also had comments on the precise shade of my shoes (from MIL), my nails (yes seriously, and I was told that if I ignored my mother I would regret it for years to come as it would show in my photographs), what the bridesmaids are and aren't doing, and a face of sheer horror about pretty much any detail that hadn't been run past them first. Oh, and faces of sheer horror about details we had asked them first about, they had forgotten about and decided that they were now just appalled by the idea.
They have made 'suggestions' that they have then told everyone will be happening. They have fussed and sulked when called out on this. (I have had this from other relatives too incuding an uncle and my grandmother).
I made the mistake of letting (and yes it was letting) my mother sort the cake out after she talked my relative who had offered to bake it for us out of doing so. I had to relieve her of that duty after she went a bit Phoebe Bouffet when she is put in charge of the cups in Friends (those of you who have seen the episode will know what I mean). So I have let her do the flowers, which I have no interest in and only she really wanted, she has found ways to still not have that finalised and is blaming me.
MIL has been put in charge of collecting cheese the day before for the evening buffet, and the conversation that we had with her over that resulted in fits of hysterical crying and shouting. About how I let my parents drive me places (they have once driven me back to theirs since I left home 10 years ago) and not taken her up on an offer of a lift that was further than we neeeded to go. Seriously. It was as mad as that sounds.
The mistake here, OP, is that I gave them nice, simple, pretty, easy jobs to do that they just decided to get totally hysterical over.
I think you need to divvy up the jobs between you and your DP (I did this and tbf it wasn't an even split but DP did have some of the big jobs). Your DP can then choose to share some of them with his parents if he wants, and he should.
Tricky jobs you may want a hand with (and its unlikely people will offer) include:
Table plan planning
Writing out invites
Writing out place cards
Calculating food and alcohol needed
Booking taxis/transport
Getting the wedding programme written and printed (though make sure this isn't used an an opportunity to strongarm you into something you don't want)
Planning logistics on the day
Emergency bride and groom kits
Ensuring the venues are accessible to all guests
Signage to venue
Then your MIL can comment on the precise shade he is wearing, and not you. She can nag him about decisions being made, not you. She can give her suggestions to him re hymns and when the two of you sit down to finalise them he can decide whether or not he wants to go with one of her suggestions, not you. She may also get a bit of a dose of reality when she realises wedding planning isn't all about choosing a pretty dress, pretty flowers and a pretty cake.
I am really saddened by some of the responses from mother's of sons on here. The fact that you think it is up to your future DILS to involve you in their future wedding day rather than raising sons who would take a bit more charge over their wedding planning than is apparently traditional. Have anyof the people criticisng the OP honestly doing considered that rather than screeching about Mil bashing?