Sorry to hear of this situation. It seems to me the DiL is possibly coercive to your son, rather than just wearing the trousers. I would be aware that he may be having a hard time of it, which is why he's like he is at the moment, especially if this behaviour wasn't the norm before he got with her. Is there anyone that he could talk to/confide in. He may be trapped and need help.
As for making comments about caregiving, I'm sure you just don't bother now as presumably she has cut you down quick in the past. However that would bug me and I would say something if I thought it would help a situation, but add "just from experience (in a lighthearted carefree way) but obviously you do what you thinks best". One day she might actually agree, even if she doesn't say so at the time and wouldn't admit it anyway. Just be ready to ignore her looks of disagreement or comments and change the subject quickly/ walk away to the loo, kitchen, garden etc - so making no big deal of it : she shouldn't be intimidating you, be strong. She may back down if you show resilience.
Regarding the freebies as others have said if its not enjoyable for you, you could just say to them (when together) that your holidaying alone this year - to allow them to sort there own holiday, as you want them to have some personal space to enjoy the time as a family - but only once you are comfortable with how you son is in the relationship and he's genuinely happy with her. Could your husband go out alone with him for man time together and see if he opens up a bit more when DiL isn't there.
Offer to baby sit for a couple of evenings once a month e.g. saying you'd love to and how it gives them a chance to have some quality time together, but only if they want you to. Don't put any pressure on them and again make it lighthearted and carefree so as it doesn't seem desperate. Most parents of young children would jump at the offer.
Just my thoughts, hope things improve for you all.