Do you not realise how controlling & manipulative that sounds? Provided the in-laws weren't racking up lines on the coffee table, leaving the front door open, slack with allergens etc I really cannot fathom where you're coming from.
Pretty much was that.
Feeding DD1 food she was allergic too after DH had said no and why - because they didn't believe in allergies - luckily DD1 was just immediately sick.
We moved house with toddler and very young baby and they insisted on visiting weekend after we went out for a meal MIL took a minute to disappear off with eldest and encouraged her to take thing off shelves without paying and out of shop area to us - as it was cute - and no one would mind - FIL has words about that with her- we had weeks of stopping DD1 grabbing things she liked when out. Another point in time less of an issue - unhelpful - but that moment felt deliberate as who would do that - even FIL was annoyed,.
Immediately DH or I said something - undermining us ie we are going home from park in 5 minutes oh you don't have to to kids so kids not wanting to leave but in those 5 minutes IL decided they were cold and were leaving and then shouting at kids because they won't leave and us for bad parenting.
We had rules and boundaries to keep everyone safe and to make life more pleasant for and if speaking didn't change IL behavior then we didn't see them as often as it was stressful and hard work - natural consequence of their behavior.
I don't think Op sounds as bad from cuddling on a sofa - but IL would try and paint their actions as innocent as possible and frankly a lot of the time is was culmination of many little things rather than massive overstep that caused friction.
OP has no power to change how her Son and DIL parent their children or how they behave just how she responds to them and the situations.
Being more mindful of their rules ( and hoping they relax with time and as their stress reduces) and trying harder to not come across as judgemental will get her further than digging in and insisting she was right.