Hey there! Can you explain a little more thoroughly what you're looking for? Do you need enemies to spawn at random times, or random enemies to spawn at the same time interval? Do you need random positioning, or just the set position?
From what I understood, you have two enemies you want to spawn at random intervals. I would do this:
1. Global variable: NextTimer = 1
2. Local variable: EnemyChance
3. Every Next Timer Seconds > Set EnemyChance to random(1,2)
4. ^Subevent to 3 - If 1, Spawn enemy 1, If 2, Spawn enemy 2.
5. ^Subevent to 3 - Set NextTimer to Random (0.5, 2)
Only one of the enemies will spawn at a time, the interval between spawns will change every spawn, and you can play with the values to fine tune the effect.