The sum of the allocation for your parents and you should be 100%. It is common (since the parents usually pay the health insurance premiums) that the parents do 100% and the child 0%. But the allocation can be anything all of you agree to so long as it adds up to 100%.
As for the SLCSP, you may be able to find your SLCSP by reading this Community thread. I believe that you can look up the SLCSP.