I see this as a few different question.
Q1. I spend my money on things like groceries, utilities, medical, etc. for my parents.
A1. For things like this I think it completely reasonable to be reimbursed from your parents, assuming they have the funds to reimburse you. Alternatively, if they don't, I think its reasonable for you to accumulate receipts and split the costs with your siblings.
Q2. Reimbursement for time spent doing the above.
A2. IMO, I'd never ask or accept money from my parent or my siblings for this. If they occasionally wanted to invite me to dinner or something like that fine. We do that for each other anyways.
Q3. Fee for being the executor of their estate.
A3. Again, IMO, no way. Now, being reimbursed for actual out of pocket expenses like filing fees, attorney fees, etc. is completely acceptable and should probably have been paid by the estate in the first place.
Personally, I consider this my repayment to my parents for the 18 years of direct care (everything from wiping my butt to driving me to high school football games) they did for me, the college they paid for, and then the next 40+ years of invites to holiday dinners, family vacations, etc. They never asked me for reimbursements, much less an administrative fee, for any of that.