The father bore guilt. Guilt for his act of selfishness, that day when he left his wife. For ten years, the feeling was like being stoned: nowhere to escape, no way to shift the load. His guilt acted as a magnet, attracting other items to his load that he simply accepted in punishment; custody battles, redundancy. The worst thing about the guilt was how it never became smaller with time. It only grew and grew until the man left behind when guilt abandoned his soul didn't know how to live.
The mother suffered betrayal. Although, let it be known that she didn't suffer in silence. The court rooms still echo with her allegations against her ex-husband. Of course all that led to was pain; but that was good enough. Her load to bear was blame that she gladly shifted onto others: first, onto the guilty man in her life (for which there was no replacement); then onto those snatched from her, lost with no defence against her wrath. In the end, she had nobody left to blame but her own mind. Her final burden was an anchor dragging her soul into the depths of despair, with her own pride refusing to sever the tether that would ultimately be her destruction.
The eldest child carried a mentality beyond her years. She spent an era carrying what she thought was responsibility: the task of fixing the remnants of what could have been a beautiful future. Instead she gained wisdom with those years, realising that this maturity was a guise. What she carried was self-loathing: acting as puppet strings, guiding her life choices to attempt to lighten the loads of the adults. Instead, she lost the most. First her family, then her ideals, and finally her own body. She was left with skin pulled taught over a template. She was lifeless, she was empty.
Since there is an eldest child there must also be a youngest. That is true, although she couldn't carry the troubles of her family through the world. Not because she was incapable, but because nobody allowed her. These burdens may have been painful, however their one remedy was love for the beautiful young girl. Unfortunately, her curse was the strongest of all, for she showed the crippled relatives that in life your soul shouldn't be carrying anything. The stunning daughter thrived; she carried the sun in her face and the night sky within her pupils- an island in the ocean of her irises. You're right, this doesn't seem to be a curse. With time, the winds changed and the thriving nature was stunted and destroyed. Those left behind gained another weight on their shoulders: the memory of the youthful free spirit of the family, whose lack of painful tethers to Earth allowed her to drift into somewhere she deserved to be.