Your question is a little confusing. I am assuming that the previous owner is holding the mortgage for him. If so, then the owner of the mortgage/previous owner is starting the foreclosure process. Just like a bank would do.
There may have been some agreement in the contract/ note your brother signed allowing the owner to do this in the event that your brother did not pay the property taxes.
Though states have different time frames and processes for collecting property taxes, it seems that your brother needs to take a look at his contract and contact a real estate attorney to help him through this rough period.
I wish him good luck
