OP,
Whilst I can understand your hurt and upset, your sister is being set up as carer for your parents.
Whilst you may feel raw from their actions, take comfort that you have absolutely NO responsibility nor obligation towards them.
That will be her job.
Now by doing it the way they have they are placing great trust in your sister taking on that role.
I know of a family that had a gorgeous valuable home on two acres.
They passed the main house over to spoilt younger son and he built a little 2 bed bungalow with a completely separate entrance etc at the very opposite end of the plot.
Within 2 years a work opportunity came up and he upped and sold HIS house for 1.4 million and is now in the US with his family.
His 3 siblings have NOT stepped up at all.
They all live within 10 minutes of their parents and or very LC or NC.
Their is still huge bitterness over what the parents did, as it was never discussed.
Son in the US very rarely comes home, never with his family, maybe a flyimg visit through work.
The parents are mortified by what has occurred as the selling up of their old home raised huge eyebrows at the time and obviously the details of what they did leaked out.
Their other children's rejection of them has been a source of local gossip over the years.
There is very little sympathy for them and those that knew their golden boy personally, were not a bit surprised.