Three months from death is hardly any time at all in a probate case.How much and what did you dad own : the house, business, shares, what ? In most cases there has to be a valuation of property and possessions, income tax returns prepared to date of death, and an extensive form completed for the Revenue, listing property and a history of any gifts made by the deceased, and much else, and any inheritance tax paid, all before probate is granted. That all takes time.
The way your stepmother talks, there's a will. That will is no use unless and until it is admitted to probate. Then the executors named in the will, (who might well include your stepmother or you) if they've agreed to act, take over and start distributing the estate according to the will.Your stepmother can't do anything with your late father's property until probate is granted: it's not hers, whatever the will says, until then. When probate is granted the will becomes a public document for anyone to read.
If there is no will then intestacy rules apply. The surviving spouse gets all the deceased's personal possessions and up to a set sum (still, I think, �125,000 ) absolutely. As to the rest, the children get one half of it absolutely and the spouse gets just the income on the other half for life