You can start by looking at the probate file or orphans court filings in the county where he resided at death. There may be some insights there.

Who gets my fathers 401k??

The short answer is yes - if he was married at the time of his death his spouse would be the beneficiary of the 401k if she did not sign a waiver. ...

Can i become the administratorof my mothers estate if one sibling refuses to sign?

As was mentioned, you will need to hire a lawyer to assist you in filing the petition to be named administrator.

How do I initiate the process of having the courts to establish the next of kin?

You probably mean that he said he had a will but you cannot find it. If you cannot find the will (or if you can and you are the nominated...

Can a trustee be sued for declining after agreeing to do the duty in writing?

Not enough information given, but in a general sense it would depend on if your actions/inaction adversely affected the beneficiaries.

How can you find out if a will was changed before or after a death of said person?

A will cannot be changed after someone's death - the person is dead. However it is possible that the terms stated in the will were not properly...

Could depend on the nature of the award (for inheritance tax, pa taxes wrongful death and survival different but that is likely not relevant) but...

You would have to see the divorce property settlement paperwork and the deed to determine how the property is owned. Short of that, anyone would be...

I have dealt with this before so I am pretty familiar with the process of what can and cannot be changed. This is not one of the standard changes....

One heir has refused to sign a release all others have sign. What can I do so my boys will get their inheritance? Thank you

As was stated, if you can't get it done informally, you will need to do so with a formal accounting.