There's a big difference between sharing of your own volition, and having someone demand you give them something. Once they steal the ability for you to offer, the dynamic radically changes.
In a popular post on the AITA subreddit, a woman asked if she was wrong for being annoyed at her SIL for raiding her wedding leftovers. She wrote:
AITA or am I just being petty over my SIL raiding my wedding leftovers. So my wedding was a Saturday and we had guests in from out of town leaving on Sunday so we had MIL take the left overs to her house to store until we could make room and freeze any left over cookies. I easily had 8 trays of food, 10 boxes of cupcakes, and 3 trays of cupcakes left.
We arrived Monday after the wedding to retrieve our stuff to take to our house only to be informed that we were now down to three food trays, three boxes of cookies, and some cupcakes. I was furious but bit my tongue until a couple days later. Turns out the SIL went and raided our stuff taking food and cookies to take home with her.
Keep in mind I allowed people to take to-go stuff from the wedding and expected what we took home was ours. The same day we picked up our stuff we also received a phone call she wanted more of our cookies and cupcakes to take to work. AITA for getting pissed off and causing a fight with my husband after only being married a few days?
NTA I could see her taking a tray or two of food but she took 5 trays of food and 7 boxes of cookies in 1 day if that’s correct? You don’t take more than half the food that someone else paid for without asking; that’s just rude.
And OP responded:
From what I’m gathering by the conversation she took it to work with her to share with her co workers.
NTA for sure! You paid for the food; you decide who gets the leftovers. SIL is an entitled AH. Draw the line in the sand now, or it will only get worse. If your spouse doesn't back you on this and address his family's line crossing (and it's his job, not yours), then he's an AH, too.
NTA this is just not done. It is consulted beforehand. And usually if even the close family doesn't offer you don't even ask. And one thing is to maybe think you are entitled to take without asking. Okay you might act on this and take one ration of each not polish more than a half of what was left and then ask for even more.
It almost sounds like the mother-in-law said to her daughter "what on earth they will do with this stuff you take it?" I mean a mother of the groom could probably not think twice and "help" her son. Or a huge spoiled princess syndrome that the sister has.
NTA. Why? Just why do some people think they're entitled to someone else's belongings? And without even asking? Also, your new husband has to start learning which family to prioritize first and that isn't his dearest sister or mother, it's you.
Update for those asking:
The food was packed up and taken to MIL’s house following the reception because she had the room at the time to keep it for us knowing we would not be able to get there until Monday to pick it up. Had the SIL asked I would have been more than willing to share it was a decent amount of food and sweets.
I’m upset that she didn’t ask us, took it upon herself to help herself, and then had to nerve to ask for more. I’m not a selfish person but I was upset when I wanted to get something it was gone.
I’ve said to my husband many times while we were dating about his sister's behavior because this isn’t the only time she has acted entitled, and he just blows it off maybe because he knows how his family is. Don’t get me wrong I love my in-laws but sometimes they really overstep their boundaries.
Hopefully, OP's husband is able to recognize this is a dynamic that can't continue long-term.