Unless you have received prior gifts and/or inheritance from your parents, then the expected amount, € 50,000, is well below the lifetime threshold of € 335,000 so there will be no inheritance taxes to be paid by you nor your siblings.
The Contributary pensions/allowances are not affected by any inheritances - they are determined solely on your PRSI record
The non-contributary pensions are means-tested - your brother and sister will have to inform the Department of Social Protection. They will revisit the contributary pension amounts taking into account any income and savings they have