How can I talk about my fiance about his mom and sister depending on him to much?

My SO and I have been together for about a year and a half. We are planning to get engaged soon. We have lived together for the past year. Before we lived together, he was staying with his mom temporarily. He’s grown 22 year old sister also still lives at home. Here is my question I would like advice on. In my opinion, SO’s mother and sister depend on him entirely too much. Now before I go further, I definitely believe you should step in to help your parents if they need help. (Mom is middle-aged, not elderly.) His dad passed away three years ago. Since he and I have lived together, I’ve noticed they depend on him for EVERYTHING around the home. From taking care of yard work to home maintenance, to even minor things like hanging pictures on the wall. They won’t even make an attempt to do any of it, even though they are fully capable. There is a lot of major work needed to do the house, and they fully expect him to take care of it physically, doing the labor and pay for it. There have been many times he had to bail mom out and catch up on her car or house payment. I’ll also mention So’s sister almost seems almost jealous of our relationship. She constantly seeks his attention and acts like a child when I’m around, horse playing like they are still kids. He’s 30 years old. It got to the point it made me uncomfortable because she was always stand-offish with me and ignored me half the time. I brought this up to him, and I guess he talked to her because it seems like it has gotten better. I also owned my own home before we got together, and we have started doing repairs on my home; for example, we recently built a porch. His mom and sister act like they get an attitude when he does things for OUR home when there are major things needed at theirs. I don’t know how to handle this, especially with us planning to get married in a year. I hate feeling this way because I know eventually it will drive a wedge and cause problems all the way around. How do I discuss this with him delicately that in order for us to move forward with our lives, his mom and sister need to stop being a burden and not depend on him for everything financially and otherwise?

He is just super close to his family. His dad was the man of the house and now he is gone. They are now depending on him and I don’t see an issue with that. The only thing I really see an issue with is him shelling out his own money for them all the time. That is something he will have to put his foot down about

How do you judge what is “too much”? Some families are closer than others. And as someone who has a great relationship with most of my in-laws (as well being with my husband since 1999), let me share the best advice I can offer: You are not just marrying one person. They come with their own history and family. So, your best bet is to treat his family as you would treat your own.
We don’t always like our own family, but we always love them. And if you take the time to build an honest and open relationship with his family, then you can talk to them directly about things instead of hinting round the net looking for people to give you the approval to do something that you wouldn’t like done to you or yours.
If you honestly believe you can’t deal with his extended family, then maybe this relationship isn’t “the one”. Because as long as you think you’ll never get along with them, you never will.