So in February my mom, aunt, and bro are all coming with me to WDW. None of them have ever been and are sooo excited! I want to have a suprise for all of them thats hopefully not going to cost an arm and a leg. Any suggestions? My bro is 14 for reference...
Disneyflorist.com has all kinds of things that you can have delivered to the room and all different price ranges. You can also make up your own basket. I have some good friends going down in Nov. with their family and I think I'll have something delivered to their room waiting for them.
Jackie 
You could also order custom tshirts for them to wear at the park, it's not crazy expensive at customink.com. I called them after I had ordered it, they said that they could sharpen the image for me, because the font I used was low resolution. Their customer service is amazing, they asked where I got the font, and fixed it up for me. I got the custom tshirt for $24. Or at the Disney store online, you can customize a shirt for them as well, that way you can have Disney stuff on the shirt. Customink has a strict rule about not using things that aren't licensed to them, such as, anything that is obviously Disney, like the mickey ears or characters. Jrangerrn brought up a great tip for disneyflorist.com! Also, don't forget to get the first visit buttons at the park! 
I agree that the Disney florist rocks!
Ok next question. If I make up baskets at home and ship them out there, would Disney put them in our room?
They will not deliver home made baskets to rooms, only treats from Disney floral. They will however hold the baskets at the front desk and put a note on the reservation that something is waiting for them.
I like to surprise the people who come with us to WDW with Disney surprises their whole trip. For example, You could buy them all "glow with the show" ears for Fantasmic one day and their favorite character as a plushie or on t shirt the next.
I also like to plan a part of each day completely around each person. If your brother likes rides you could plan one day at HS. Make the morning and early afternoon all about him. Do all the rides for him. Do everything he wants to do for part of the day. If someone in your party loves shows, the evening could be for them. You could see "beauty and the beast", "the muppets", "the voyage of the little mermaid" and Fantasmic.