Inheritance tax due on real property can be paid in 5 equal annual instalments (interest is charged of course!). The first payment is due one year after the Valuation Date. This might give the sibling some time to breathe.
Then if the property is sold before the due date of the first or any subsequent instalment the taxpayer must pay all the tax outstanding at that point. I'm not sure what the interest rate on instalments is, a bit higher than a bank I would guess, however, the fact that the first instalment is one year after the Valuation Date is an option, allowing a bit of time for things to get sorted in the estate.
Also, Revenue have powers to compound and postpone the tax, but that is usually only in cases of severe hardship where a person would be forced to sell their home to pay the tax.