The other 100K of gain's tax rate depends on where his other income is at.

Don’t be afraid to ask for lower rate, especially if you find the house or FSBO, in writing in the agreement, and that additional fee they’re charging would just make me angry.

One thing to also consider is if the kids take it over will they jack up the rent to market rate?

Or interest rate caps, or partnership level expenses, etc.

Now I am investing in the US and a few of them have offered to lend me money at a set interest rate that I will use to grow my US real estate portfolio.  

Due to less competiton and less transparency, are commission rates higher, lower or the same in commercial? 

Interest rates will skyrocket, as inflation comes back. 

I could theoretically get my money and rehab costs back in ~ 1 year assuming it rents for $1500 per month (current market rate).  

The IRS still doesn't like "short term" 1031s, with good reason - you need to ensure that you can 100% support that it was not a flip.This was not uncommon during 2020-2022 when prices were increasing at an incredible rate, I did have a few clients where they acquired a property that was truly intended to be a rental property, had a long history of buy / renovate / hold rentals, and then the market just blew up so fast that it changed the investment analysis for that property, or in several cases they actually just received unsolicited offers that they couldn't refuse.  

Realtors can compete on commissions, or even offer a flat fee transactional rate for service.