Sounds like it is all non-probate so a probate estate would not be needed. Although you may want to consider his debts if any. You are correct that you would want/need to file a PA inheritance tax return. If there is no will the inheritance taxes will be charged on a pro-rata basis to the beneficiaries of the accounts, however, you may benefit from deductions (funeral expenses, tax prep fees, etc.) if you file a return rather than have separate bills which are sometimes generated in these situations. The different classes of people inheriting (child, nephew, etc.) have different tax rates. At the least you may want to consult an attorney or tax preparer (but only a tax preparer with experience with PA inheritance tax returns).
This is not legal advice nor intended to create an attorney-client relationship. The information provided here is informational in nature only. This attorney may not be licensed in the jurisdiction which you have a question about so the answer could be only general in nature. Visit Steve Zelinger's website: http://www.stevenzelinger.com/