In general:
1. If you are a US person for tax purposes (citizen, green card holder, or resident alien) you are required to report ownership or control of any foreign account that is worth more than $10,000US at any time during the year. This is not taxable, but it is a reporting requirement.
https://www.irs.gov/businesses/small-businesses-self-employed/report-of-foreign-bank-and-financial-a...
2. If your mother sold property that your mother owned, then your mother owes income tax according to whatever tax laws she is subject to, depending on her status. She is probably liable for tax in the foreign country. She will also be liable for US tax if she is a US person for tax purposes (citizen, green card holder, or resident alien).
3. You are not subject to any US tax on the proceeds of the sale, as far as I can tell. It's not your income. If you are just holding the money temporarily, it's your mother's money. Even if you keep the money, that is a gift from your mother to you. The taxable part of the sales proceeds are taxable to her, not you, because she owned the property, not you. Her giving a gift is not taxable in the US, and you receiving a gift is not taxable in the US. If she is a US person for tax purposes, she must report any gift of more than $17,000US per person per year, but tax is not owed unless her lifetime total of gifts is more than $13 million. Whether she owes gift tax for making a gift in her home country is up to the laws of that country.
4. You are subject to income tax on any income you earn from the money while it is in your possession. For example, if you converted $25,000US to the equivalent in bitcoin, and then converted it back to cash for $26,000US (because of changes in BTC valuation), that $1000 is taxable income to you. You also owe income tax on any interest paid by the BOA account.
