If I already offered them these two options via text/phone, and I start the 60-Day notice vacate tomorrow, can they use this against me?

I us a property management app to receive less phone calls from tenants and collect less rent in person.I am trialing a couple others, I will be glad to let you know what I decide to go with if I find one better. 

If you are doing it alone, why not pick up a phone and call them and be like "hey" the lease notes rent is due the first, I know there is a grace period on this but I would appreciate it if you could make the payments on the first?

That's probably "phone book". 

When I replied back to their email asking when I could pickup keys to assess the situation, she doesn’t respond to email, nor she pick the phone, nor responds to text.

I would collect guest data for 1 year (phone and email) and then have a direct booking site and a marketing campaign to previous guests to book direct. 

I can't post phone numbers here but you can find them with a quick google search. 

Actually TALK TO THEM on the phone and/or in person, find out about their situation, and if they seem like a good fit, basically just be smart about it, and have human interactions with them, it's that simple. 

I've personally tried to contact the former tenants and ask for the receipt of the utility bill, but their phone numbers have changed in the meanwhile and I've had no luck. 

But what about this option - you get on the phone with the individual and a realtor and let this person give the realtor access.