“I am only one,
But still I am one.
I cannot do everything,
But still I can do something;
And because I cannot do everything,
I will not refuse to do the something that I can do.”
The cancer impacts on the siblings' lives also. Family life changes drastically. For example, they don't see their sister/brother for weeks on end (other than maybe by Skype) while the sibling is in hospital undergoing treatment and one parent is always at the hospital with the ill sibling.
This link gives in-depth information and help regarding the subject of how cancer affects siblings: