Salam - Struggling with my sister‑in‑law’s behavior and where to go from here

Salam everyone, I’m 23 and my husband is 24. We’ve been married less than a year, and before getting engaged we only knew each other about a month. My family is fully Pakistani and we were raised with our deen and culture. My husband is half Pakistani, half white and didn’t grow up practicing much, though he’s moved closer to Islam in recent years. When I first met him I assumed he was very religious, but as I got to know him I realized he isn’t as observant as I thought. His family similarly aren’t very religious. Growing up I always planned to marry a Pakistani man; he was an exception because I felt I could do it for the sake of deen. As I spent more time with him and his family, I noticed many things that make me uncomfortable. He has one sister and their boundaries are almost non‑existent. She’s taken photos of him in just underwear, wears revealing clothes around him, talks about secret trips with her non‑Muslim boyfriend, and he hides much of this from their parents because he’s afraid of losing that friendship with her. She walks around the house in a bra and shorts - things that would be completely inappropriate in my home. On family trips she insists we all share one room - me, my husband, her and their father - and says me having a separate room with my husband is a waste of money. My father‑in‑law goes along with it because he’s always trying to save. She’s disrespected me a lot; one time it escalated so my husband had to raise his voice at her in front of many relatives. She also complains that they spend too much on me, yet they didn’t give me proper gifts or pay my mahr fully - my mahr was set very low. I’ve told my husband many times that their relationship is not normal and makes me uneasy. I wouldn’t want my future children to be close to her in the same way she is to him. When I ask my husband to set firmer boundaries, he gets upset and accuses me of trying to take him away from his family. Situations like this make me sometimes wish I had married into a more practicing family, and I hate feeling that way. There are other issues too - they have us join their Christmas celebrations, go to beaches in ways I’m not comfortable with, and because my husband is in medical school he’s financially dependent on them and afraid they might threaten to cut him off. They’ve even told him he spends too much time with me, even though he comes home only every few months because of school. I don’t really know what to do. His parents often act stingy, push him into things I dislike, and give comments like I see him too much or drive him around too much. May Allah ease this situation for anyone dealing with something similar. Allahuma ameen.