I could help explain what you are after but Biggerpockets has some really good books on the basics of real estate investing and for a few dollars you can get a ton of knowledge.

I have a video on my youtube channel explaining. 

Offer them a chance to explain any difficulties they may be facing and discuss potential solutions.

I've explained that I have the advice and strategy side covered.

I'll send you a video that explains better

I explained to them my limitations and approach but they threaten to not pay because they do not believe the bill reflects their usage.

explain nicely

Since I am new to this I don't fully understand the lingo, can you please explain REI, and ADU?

More then willing to explain what we do if anyone wants to chat.

Here's a PARTIAL list:Office rentComputers, printers & softwareInternet & phone billOffice furnitureOffice supplies: paper, postage, ink, etc.Office liability insuranceAuto expenses: monthly payment, insurance, gas, maintenance, registration/plate feesBroker license fees: annual, monthly board & MLS fees, continuing education fees, E&O insuranceEquipment: lockboxes, signs, etc.Payroll & payroll taxesBusiness income tax preparation and paymentsLabor: answering phones, calling past due tenants, scheduling tours, taking marketing pics, processing those pics, writing ads, researching rent amounts, posting ads, explaining to owners how rent determined & showing where ad posted, opening & processing mail, posting payments, bank deposits, scanning documents & posting to owner & tenant portals, explaining accounting to owners so they understand their monthly statements, taking pics/videos of repairs, finding reputable handymen and contractors, confirming they're properly licensed & insured and tracking annually, verifying repairs done properly, processing invoices for utility bills, repairs, taxes, city inspections, scheduling periodic property evaluations/inspections with tenants that don't want strangers in their homes, explaining to owners why taking so long, and more & more & more...