What we can tell you most simply is that your story is quite similar to many, many other humans and, in fact, most who have had difficult times with family members, and this is spanning multiple lifetimes of interchangeable roles and encounters where things did not always go smoothly—promises were made but broken, there were tests of strength and will and quests for power to manipulate the parents on the part of siblings, and so on. These do leave a mark and when even worse things happen there is a demand for much healing to happen to rebalance the errors of the past. That is often a reason for people to come back together in family settings to share their experience of being a part of this unit and to work on correcting and rebalancing the negativity of the past.
That is mainly what you need to know, that you are involved in a healing effort rather than hear the specifics and the gory details. You can reinforce the effort ongoing by doing additional prayer work on behalf of your family members as well as yourself for the healing to be effective and complete and to bring each person a chance for them to be their highest and best version of themselves as a result of the divine healing underway. This will reinforce it and speed its progress. These can be very long-term efforts needed because the karma is often extensive and covers so many parallel lifetimes of difficulty. This is the average situation, not an extreme case, but nonetheless there is much to do, much to make up for, and this will take some time, so you needn’t overworry about this. It is perfectly normal and the reason for reincarnation with the same troubling individuals and histories—it is to set things right. You are getting divine help with this and it will make the difference over time. There is work being done on your family members in parallel.