I'd buy for each person equally. I mean, I'd set an amount for my total and either divide it between all 9 or I'd set an adult amount and a child amount. Why would the unmarried daughter expect to get the same total as the family of eiight? If she does, you've made a mistake somewhere along the way.
Oh, and I would not go crazy trying to make it exactly equal either. My MIL goes extremely nuts working to give everyone the same number of packages and spending the same amount. It's not unusual for her to give someone a few dollars and cents to make up the difference. Geesh! Don't do that!!!
Oh, and I would not go crazy trying to make it exactly equal either. My MIL goes extremely nuts working to give everyone the same number of packages and spending the same amount. It's not unusual for her to give someone a few dollars and cents to make up the difference. Geesh! Don't do that!!!
I paid for and supported myself thru school, work for a top consulting firm, bought my own condo in downtown DC on my own (saved my own 20% downpayment, unlike sister) took the whole damn bunch of them on vacation to WDW this year with deluxe hotels, tickets, airfare and all meals. Have made SIX trips home to see them at my own expense. In the 5 years I have lived away they have not once come to see me, but yet they have traveled to see sister six times THIS YEAR to see her. Before you are too quick to jump, my sister lives away too and she hasn't been home since last Christmas so it isn't like she is doing it all. I even took a week off of vacation to help them go thru a lifetime of house possesions so they could move. Sister didn't do a thing towards it. So PLEASE tell me how I could possibly be a disappointment. 

It is favoritism and bias. 
Oh, please. No one is punishing you. Your parents are doing what they choose with their money. You made your choices, are you happy with them? If so, why don't you stop trying to find something to be miserable about and enjoy your life. If you are not happy with your choices, make new ones. 