There are many savings accounts that pay 2%+ such as American Express, Ally, etc.

You could use that as an intro, to express your interest and gather information (ie, is there a mortgage, any other liens, are taxes and HOA up to date, etc). 

Hello,So we've been talking to our landlord about possibly buying one of his properties (he has offered to take a percentage of the rent we've paid and apply it to closing costs).He told us he has a 5-plex he might be willing to sell (it's not officially on the market).What should be the first steps we take in expressing our interest in buying it and doing due diligence?

Real Estate Express, I did mine in NYS through them and quickly at that.

However, she has expressed that she too has wanted to own rental properties but doesn't know how and thus the idea of becoming partners has come up.

Hey Nick,I'm a fan of Real Estate Express. 

I mostly get deer in headlights or glazed over expressions from folks that can't comprehend all that goes into this or who find it exceedingly boring.  

Your responsibility should be to yourself, not the applicant.If they express interest, I tell them they are welcome to apply but I will continue marketing it to others.

Don’t be afraid to express your concern.

I continued to be astounded that we were all stuck in a prison on death row and I just found the master key to every lock, yet as it turns out, all these years of hearing how no one wanted to be in prison was just a way of expression their discontent on how the prison treated them, not a true desire to escape.