It is a court proceeding, it can be done in most states, including yours. It's probably the best way to take care of your sister now. This way, someone can make decisions for her, her medical decisions, and the proof is that she is unable to take care of herself.
The same with the conservatorship. The proof is that she is unable to make financial decisions for herself, and I'd especially worry about her husband too. Sounds like he's someone who is making her life more difficult. I am really sorry about that situation.
You can start a proceeding for a guardian and a conservator. It doesn't have to be you if you don't want to get entangled with the husband. You can ask that someone else be appointed.
You'll want to use a family lawyer for this but it can be done and is probably one of the nicest things you can do to protect your sister.
If you need names of lawyers in your area, just let me know. Can you do this yourself? Probably, but you're going to need some help with forms and if you are willing to look online for forms and also talk to the court clerk, you can do this yourself. I don't necessarily recommend it, but it can be done this way. It's up to you -- if you're able to do this with an attorney, that's great. If there's nobody else who can file this, then you should be the one filing, but you can still ask for someone else to be appointed.