It certainly sounds like you’re being taken advantage of. But, this isn’t their fault — it’s yours. You’re allowing it to happen.
You need to be perfectly clear with them (and yourself) when the move-in date is, what the rent is, and what the deposit is. The deposit should be paid now (or at very latest when the lease is signed) to hold the spot for when they’re ready to move in. The lease needs to be signed immediately. And the first month’s rent needs to be paid when they get the keys, which should be the possession date on the lease.
Don’t be willing to change any of these terms, especially since you seem to have a lot of other interested potential tenants. If these tenants can’t live up to the terms you’ve set forth, dump them.
Being a landlord isn’t overly complicated, but it does require that you be willing to be inflexible and put your foot down when someone takes advantage of you. If you can’t do this, perhaps find a property manager to manage the property for you.
