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1. promissory note

You can google online for a PDF, fill out the numbers and sign it with a local notary and mail to your brother. In case you die, your brother can rely on this note to participate the division of your estate (遺產) 

2., estate tax = 遺產稅

Assuming your brother or his kids are not green card or US citizen, just foreign nationals.  If they own the house and if they die, the house is their estate (遺產), only 60K is exempt from estate tax of 40%.

The exemption for US persons are 5.5 million, but the exemption of estate tax for foreigner is only $60K.  So if the house is 1 mil, $940,000 are subject to 40% estate tax.   

https://www2.deloitte.com/content/dam/Deloitte/us/Documents/Tax/us-tax-us-estate-and-gift-tax-rules-for-resident-and-nonresident-aliens.pdf 

It is probably worth it to have consult an estate lawyer before buying a house in US.