[Snip]
Oh them being siblings doesn't mean it's just okay, but (most) siblings are close enough or care enough for each other that such questionable actions are less offensive because they can trust each other to not act with intentional malice.
This largely depends on how dysfunctional your family is, --in some cases-- if one or more siblings has bothered working through any of the childhood crap, and in other cases if the one who got bipolar disorder and is borderline schizophrenic has acknowledged either and gone to a psychiatrist for help[1].
It usually is, my mother is a good cook 😊 She does tend to get a bit passive-agressive about how much work it is, and how much time she spent in the kitchen, and that it takes a day to do the cleanup... So this year we put our foot down and divvied up the tasks 😉
Everybody helping definitely helps. Learning how to cook your favorite dishes is also nice. So much knowledge has been lost already, so hang on to some of it is good. Even if it is just the perfect stuffing recipe.
[1]We all three got the hereditary depression issues, one's also boarderline schizophrenic (amongst other undiagnosed issues), and somehow I managed to be the only one w/o bipolar disorder. Yay just being depressed! ....Wait. Shit.
EDIT; I've been recently informed that my older brother only has mild depression. Apparently the mood swings were bog-standard alcoholism. Thankfully he quit drinking.