We have already started proactively talking to the tenants about some of their options and the ones that have reached out I have been trying to connect them with some jobs that may still be available (work from home data entry, virtual type jobs in health care, delivery drivers, etc.)It's going to be a rough few months I'll say that. 

Grocery workers, bottom-rung health-care, delivery workers, are all mostly in C'class housing.

All you need is delivery confirmation.

And if the tenants intake the delivery you know they will claim no responsibility if something breaks or it doesn't work upon opening.Do I want a warranty claim yes, I do. 

Your matter of fact delivery seems like the least confrontational way to handle things.

All future communications should be through methods where you can document delivery and receipts of your communications  Regarding cash for keys, $200 isn't very much.

You don't need a signed copy when you just give them 30 days notice of new terms.Then, send it with tracking, so you have proof of delivery. 

I do not know about your area but where I live providing a cluster box is the responsibility of the post office as it is their decision not to make door to door delivery. 

I would just mention mail / fedex/ UPS delivery was asking at  the house for the sister and ask why.

I always figured if it was delivered with delivery confirmation, without required signature, that was good enough.