The plumber sends a bill to manager for $100, and they pay it from your account.  

@Danielle TranI am a loud critic of transferring properties to LLC’s when it is residential, but for commercial properties I do recommend those be held in a LLC.I would speak to you accountant and an attorney in regards to understanding the tax consequences as well as the attorney regarding liability of the commercial property.

As mentioned above all trad accounts come out as income in the future. 

Since filing is open for the IRS do it online digitally.

Also, if you setup a servicing company to manage the payments (usually like $25-35 a month), they can setup an escrow account for taxes and insurance as well and cut a check to her Trust bank account each month.

If after the funds are paid into the business account and my friend writes a check to their personal account from the LLC to get his money out, are there any accounting implications?

Someone once said that keeping money in retirement account (401k or otherwise) will cause you to be poorer every year as you live on it and withdraw $$ from your account every year. 

An accountant would help here, as you can make gifts to family members every year to a certain amount tax-free.Finally, you could simply sign over the dead to your son, if you trust him to pay you back over time.

We already have a shared personal bank account.

There are also additional costs of operating and maintaining an LLC, like separate bank accounts, annual report filings, tax filings, etc.2.