Hi Piddock07,
That's quite the unfortunate predicament, with many family dynamics going on within the background. Well let me first say that it doesn't really change anything if the sister doesn't consider you part of 'her family' as you have already integrated into the family via marriage and children. Honestly one can say that she isn't part of "your" family, so don't let that particularly comment dislodge your image of where you realistically stand. You are one of the major backbones, she is just showing her unique personal colourings and let me ensure you, it's definitely no Vincent van Gogh or Rembrandt.
It sounds like your husband is too emotional attached to the mother, to such an unhealthy extent that your general opinion doesn't hold much sway compared to hers - please do correct me if I am wrong and apologize in advance. If your husband is troubled by previous childhood events and is letting this regrettable trauma influence certain relationships, which in turn allows the mother to persuade her son for certain goals then I suppose something needs to break that cycle. But avoiding escalating conflict should be one of the key perimeters when approaching this matter with your husband - showing strong emotions will only make the situation worst and could even push your husband back from listening to you. Be proactive and not reactive. A discussion with your husband will need to take place and clear examples for his mother's behavior pointed out, without being structured as petty. E.g. While I do respect and admire your love for your mother, I sometimes feel as if my opinion is being overshadowed by hers. E.g. I feel that some of her previous actions are having more negative affects to our family and that we may need to sometimes distant ourselves from these outcomes. Have less direct involvement but you can still provide some emotional support of course as long as it's not breaking any set boundaries.
Remember you don't need to be friends nor even like your mother-in-law; it's just more ideal if everyone does get along. It seems like clear boundaries and emotional/physical distance will be require, make sure your spouse knows it's okay to maintain a bound with his mother without involving you as long as anything like financials or plans are passed through you too. Either way something needs to change, he needs to listen - this is both for you and your daughter. A counselling session may even assist but I would avoid involving your daughter too deep in this, children are very impressionable things and do tend to blame themselves for whatever occurs. They are good at finding ways to do. But....if he doesn't listen and you have tried everything within your power... then maybe...perhaps considering an separation might be in order. It will be difficult at first but could avoid dealing with more dramas directly in the future, it all depends as nothing is certain.
As for the 'Colourful Sister', she shouldn't be exposing your family or daughter especially, to any illicit drugs and if she does, may I recommend prohibiting her from seeing your child until she realizes this is not acceptable behaviour and can endanger your child. If this is an issue with your partner highlight this concern with him, it is not a big ask by means. It is an basic requirement - it's all about what environment you wish to create for your child. You deserve to be treated with respect and if she cannot achieve this simple task then maybe distancing yourself could be ideal.
Have you considered looking up techniques with dealing with toxic mother-in-laws? I'll show some example, just in case.
https://www.psychologytoday.com/au/blog/mate-relate-and-communicate/201311/how-handle-your-monster-i... - Psychology Today - How to deal with an monster-in-law
https://toxicties.com/toxic-mother-in-law-signs/ - Toxicties - Toxic mother in law signs
https://www.quora.com/How-would-you-handle-a-toxic-mother-in-law-sister-in-law - Quora - How would you handle a toxic mother in law sister in law - Someone's personal experience
Please let us know if you have tried these approaches or how it generally proceeded. Many people have dealt with these situations before, it is not uncommon.
