I suggest finding support groups and maybe organizing a sit down talk with you and others. If you don't think you can try and just tell your in-laws you're worried about you SO, maybe try getting them help

As someone who has struggled with this in the past/ continues to struggle with this issue, I can tell you that setting expectations in a setting where they don’t feel attacked can maybe sink in. But the unfortunate thing about this stupid disease is that once it gets to that point, nothing will change unless they decide they need it to change. And they may not feel they need it to change until they hit rock bottom. And everyone’s rock bottom is different. Mine involved a DUI. Many of my family member’s was death. But maybe getting arrested is a wake up call. But if it’s beginning to be a danger to you and your loved ones, I would recommend removing yourselves from the situation. You can be supportive from a distance, and set the expectation that you’ll be doing so until they get sober. My dad used to drive drunk with me all the time, and my mom only left after he got so drunk he got a shotgun and was going to murder/suicide everyone in the house. You cant change or control them

Hugs! I don't have a lot of advice, as you seem to be quite dependent on your SO right now. Is there a way to improve your independence? A job, no matter how small may give you an income, but also a social network of people to help you. If your partner is truly addicted, getting him out of that is not easy. A DUI is probably not going to stop him drinking. Find other people who care for him, and can help you witj bringing tje message across that you are worried about him. Maybe they can help with finding ways to relax without alcohol. Can you work together in eliminating triggers? Support groups help, but I think that addicts will usually burn a lot of bridges before accepting that they need help.

Join a local Al-Anon group. Others have been through the same kind of things you're going through, and they can help you with their experience.