What should I get my little sister and brother for Christmas?

My money around here is scarce, and I have 2 siblings to take care of, so I am in a tight situation here.My little brother is 11, and my little sister is 8. Just so you know, my sister hates little girl things like Barbie and Dora, and my brother is way out of the robots, space, and dinosaur age.They are really important to me, so I need to get them the best gifts possible, on a tight budget scale.Thank you so much for your help. Merry Christmas!