Accept Some Siblings are Duds
Rather than trying to 'fit' selfish siblings into a box of "You should help out....." why not move beyond that? And realize that some siblings are just awful and have no intentions of being decent, helping people.
Once you go into the zone of NOT expecting the siblings to change you free up a lot of energy (that would otherwise go to resentment) to just get on with the tasks at hand.
And long after the parent is has passed on you also have the choice (or not) of having very little to do with the selfish sibling; if they didn't care much when your parent was alive, why care much later?
Whatever they were as a non-helping sibling will not change after the death of a parent.
Cultivate friends who are good souls and gather people around you who DO have caring hearts and hands is the advice.
And cut-free the useless siblings. Sayounara! See you (or maybe not) in another life time.
Life is too short to waste your time making deviant siblings into decent people; they aren't and won't go there. Sad but true.