YABU, if it's only for special occasions, presumably no more than every couple of months.
Also dh BU for not helping out more.
Also depends on time of meal, if meal begins quite early then probably ok, but if it's 8.30 booking then your in laws are BU.
We regularly take ds (2) and dd(6m) to restaurants as my in-laws are the same. They would book restaurant for about 6.30 so dcs get tired at the end, but are ok most of the way through.
If your ds is active, make sure he gets lots of exercise throughout the day and don't sit him up til the meal starts. My son is also active, but is now used to the idea that he has to sit up for most of the time and can't run round the restaurant. We bring stickers, books, crayons, etc, and take it in turns taking ds for a walk to the toilet/restaurant garden/down the road if necessary.
Good tip is to make sure ds is not sitting next to you. Sit him between dh and mil, so they have to deal with him. or get adults to switch places between courses so it's not you all the time.
Better to train dcs in how to behave in restaurants when they're very young, I know people who have 6 year old who can't behave in restaurants so they can never go out as a family.
And don't worry about other people in restaurants, even smart restaurants are fairly noisy with conversations going on at every table, ds probably not heard over the din most of the time.