Can they forclose on my late brother’s property?

Had anyone notified the lender (whomever foreclosed) that the house was in probate and who the heirs are? If yes, then they should have contacted you and the other heirs and given you a chance to respond (to pay the amount due; to raise a legal defense, if there was one, to foreclosure, or prove factually that foreclosure was not legally warranted--such as that the loan had been paid in full). A failure to have done so can provide a basis to set aside the foreclosure, though if money is owed, you have no intention of paying it (or ability to pay), and there was no fundamental defect in the mortgage, such a reprieve will only be temporary: if money is truly owed on a mortgage or HELOC and not paid, then the lender can foreclose. In this context, if any money were owed, it all became due in full when your brother passed away.
But if no one contacted the lender and told them that the estate was in probate or who had an interest in it, they had no obligation to contact you: you (the estate or the heirs) must reach out to them and update them as to status and who has an interest in the house. The lender has no obligation to try to find out if anyone else has an interest and, if so, who they are, where they live, etc. A failure to provide information/notice about the situation vis-a-vis inheritance to them eliminates in turn their responsibility to provide notice of the foreclosure to you. In this case, their failure to provide you notice or contact you is irrelevant and does not affect anything.