What is normal for others in terms of inlaw relationships does not necessarily apply to you. Don't crowdsource that question. What other people do is not going to apply for the most part.
Instead, consider your motivations. What I am reading from your post is that you are holding back on helping out with finances because your husband's sisters are going to get inheritance that you are not going to get - and that is already established. Plus you have young children to feed.
If I were you, I would hold onto my own money for my own kids yet remain as respectful as possible. Visit India as you would like to. Stay where you are invited. If your husband's sisters don't invite you, stay nearby and have coffee or something and don't give them a second thought. And then when you go home you can hold your head up as having been the bigger person. You don't need to spend a lot of time with them, and then it will be done and you can move on with your life.