Well you enemies have to be assigned to variables, so just use rnd in the range of those enemies and do it a set number of times(how many enemies you want)
I totally got carried away. I was gonna make a small bit of code to show how to initialize your enemies and wound up making a mini game. Too long to post the code but it should be fairly easy to follow and show an example of what you are looking for. I opted to use spvar instead of parallel arrays but it isn't really all that different either way. Anyway, the key is 5K4KNPA6 assuming I uploaded ok
In your code, you shouldn't be looping over random numbers between 0 and 9999 in a double nested loop. instead x should be a random number between 0 and screen width, and y a random number between 0 and screen height. you only need one loop between 0 and 19 where you initialize each enemy as you go. Hope that makes sense. My demo key above has a function that does about what you are looking for.
Actually, I suck at smilebasic, That is just part of what I learned at khanacademy.com's computer programming/computer science course. lol! Glad I could help!
