@Gui Qiu,  You will definitely need an experienced professional to set this up.1) Property owned via foreign Corp : 2) Property owned via foreign Corp via US corp: Both of this will avoid estate and gift tax. 

Your son would be the initial minority holder.Have your lawyer set up a strong operating agreement that will not only provide asset protection but also keep your son as a non decision maker even if his shares interest increase in the holding LLC, making you the one in control.Every year, gift tax free to your son more interest in the holding LLC (up to the gift tax exemption fair market value).This holding LLC will file a 1065 and issue a K1 to all members.

Maybe offer half-off rent, or maybe offer to throw in a  $200 wal-mart gift card, something for the holidays.. for the right price/incentives, things can be rented!   

You'll also develop an appreciation for how little really good finishing work happens in this country, and how many dudes who pretend they can do this well are not gifted with quality tool-using genes.

Yes, the estate can and should pay the mortgage to preserve the asset.If the named beneficiary does not want the gift, they would disclaim the interest in writing pursuant to local law and it would then pass to the next named heir or as part of the residuary.

You can buy a gift card.

Our deal was he was giving me the 3000 as a gift and I was going to sell my old car for about the same exact price m. 

The rent is the rent.. period.I would however compensate them for the hassle....gift card to dinner, movie, amazon...whatever.How much depends on how big of a hassle they went through and how long.

If they complain to you about a guest problem (noise, whatever) apologize, deal with it, then send them a big gift basket or something.Better yet, run your STR somewhere without an HOA

Baltimore, the gift that keeps on giving.