thats really not gonna be big enough for multiple turtles for life imo.
Maybe a single smaller turtle species (like a stinkpot) in a 40 breeder. would be do-able. The info in this thread is old and was never very good tbh, a 30 gallon tank won't be large enough in the long run.
If you want multiple turtles, I'd get a 75 gallon at least. Petco has their tank sale going right now, a brand new 75 should be about 86$. Or can usually find them used cheap.