30th For Parents.im Only 15! HELP!

My parent`s 30th anniversary is going to be May 15 and I really want to throw them a party. Problem is I am only 15 (I`ll be 16 in April).If my brothers like the idea of throwing them a party Im sure they`ll help. They are all in their 20s.
I want to keep it small, immediate family. Neither of them really talk to their brothers and sister, with the exception of a couple (they have alot). There is not alot of ideas that I can get from their wedding. They were married in MX and I have only one pic of their wedding. I dont even think they had a reception. My mom is always throwing a party for someone so I really wanted to do this.
For the food I wanted to make their favorites (which I was investigating tonight).Of course Im sure it`s not going to turn out like how my mom would have made it. I want to ask one of my uncles if he would help me out by making the cake. My mom likes cheesecake and my dad likes lime cake.
I wanted to throw it in the backyard, but I need a way to get them out of the house. I also dont want too much attention on them because that would make them umcomfortable.
I would really like if someone could give me some ideas on how to make this work. Color theme suggestions? Please give me some constructive critism! I only have 2 months! Thanx :-)