You really need proper, specific, personal advice but in broad terms:
1. On your fathers death on intestacy, your mother took 2/3 (80K) and 6 offspring took 1/3 ( 6.66K) each.
2. Your mother extracted a Grant but has since died without administering the estate so a second Grant needs to be taken out to your fathers estate.
3. I think someone ( the same person as above - probably you) will also need to take out a Grant to your late mother's estate.
4. Of the 2/3 interest you mother inherited she has left you a life interest in the property and there is a Revenue calculation to work out that value.
5. Of the 6 siblings, you are entitled to 1/6 of 1/3 of your fathers estate and a life interest in the 2/3 interest held by your mother. The remaining share is held by the remaining 5. 4 will "gift" to you or "disclaim" their share and you will buy 1 out.
There will very likely be a cost to you in terms of professional fees( unless you decide to d.i.y.and given that it is complex I would not advise that) , Probate Tax, CAT and stamp duty but much will depend on how you handle it. Is this your only residence i.e. is this where you live?
Depending on your age, other assets, debts etc.,etc you may be able to raise a mortgage for the costs on the security of the property if it is to all come to you in the end.
mf