Sorry for your loss.
The first priority here is access to money to pay bills. Presumably your mother will act as administratrix in the estate and it is possible for an adminstrators account to be opened in the bank where your father had money- she should first of all try to get access to his funds as administrator to pay the bills. If the bank will not agree, the account can be set up as a loan account to be repaid on the granting of administration, and again, depending on the amount in your late fathers account, either look for an offset or a low interest rate.
Because there is a farm involved, and an intestacy and children under the age of 18, my professional opinion would be that it would be unwise to try to do this administration yourselves and you should get professional advice- now having read through the previous threads, you should know enough to insist on getting a quote in relation to the basis of calculation of legal fee upfront so that you have a good idea as to how much it will cost. If in doubt, shop around, but having said that, the cheapest will not always be the best, so rely heavily on personal recommendations too.
In relation to the inheritance from his aunts estate, presuming he survived his aunt and then died, this inheritance will still be passed on to his estate. It will not delay your fathers estate.