The only recourse you have at this point is to come up with the full reinstatement amount, or have a bona fide sales contract to sell the property prior to the foreclosure date.   

(g) A bona fide lender for value without notice accepting a voluntary lien against the real property to secure the adversely possessing cotenant heir's indebtedness or a bona fide purchaser for value without notice may conclusively rely on the affidavits required by Subsection (c) if:(1) the affidavits have been filed of record for the period prescribed by Subsection (e); and(2) a controverting affidavit or judgment has not been filed during that period.

But I'm surprised that no one has already mentioned a simple appeal to logic here:  it should be stated quietly but firmly and often that a bona fide purchaser (that is, you) is interested in acquiring this physically and monetarily distressed asset for a reasonable, already-negotiated price, and that the Brother has the choice of accepting that price, or getting wiped out and receiving literally nothing.  

@Cody SteckIf you market the property without legal title and not "acting agent for" with a bona fide listing agreement, then you are breaking the law.You can market the "option to purchase" because you own the option (optionee), unless the optionor has prohibited it.

In order to establish whether a particular gift of down payment money is permitted, we have to examine what the FHA describes as a bona fide gift.

That's why it is important to have the house inspected by a bona fide inspectors.

If this is a bona fide paying tenant and I am again assuming this is a rental dominated neighborhood with all that comes with it in these areas then as I said it would be absolutely stupid for the seller to kick out a paying tenant for all the reasons you suggest.

In theory you could go into their unit and take/damage their stuff, but legally you can't go into their unit whenever you like (you've sold the right of entry/possession in exchange for rent) and in most states you have to provide advance notice except for a bona fide emergency.

And good luck reversing the next transaction... if it's with a bona fide purchaser for value (often thru a different title company, so no notice unless suit/lis pendens has been filed) you are SOL. 

Equipment Lien means any security interest, financing lease, personal property lien, conditional sales agreement, chattel mortgage, security agreement, title retention arrangementor any similar arrangement (including any related financing statement) for Tenant’s acquisition or leasing of any Financed FF&E used in the Premises that is leased, purchased under conditional sale or installment sale arrangements, encumbered by a security interest, or used under a license, provided thateach Equipment Lien encumbers or otherwise relates only to the Financed FF&E for which such secured party provides bona fide purchase-money financing or a bona fide equipment lease, after the Commencement Date.