A: From the information given, it appears that the best thing to do to protect against capital gain tax on your mother's house after her death is to do nothing. If she holds ownership of the house until her death, there will be stepped up basis for calculating capital gain. That is, the capital gain would only be gain that occurs after her death. If the house is sold soon after her death, there will likely be no gain at all.
A: It is fairly simple to renounce your right to administer an estate in Pennsylvania. You fill out form Orphans Court Form RW-06 (you can download it) including filling in who is agreeing to administer the estate in your place. You have to sign the form in the presence of a notary. You give the signed and notarized form to the person who will be petitioning to administer the estate and then they include that with their own petition and documents to open the estate.
Note that if the person who ends up administering the estate is a Pennsylvania resident, they will probably not need a bond as long as all the heirs entitled to inherit are over age 18.
A: A guardianship of a minor's estate is required if the amount of the minor's assets exceeds $25,000.00. A guardianship of a minor's would be established by petitioning through the Orphans Court Division of the Court in your county.
It is important to note, however that while you can file the petition to appoint a guardian, under Pennsylvania law, the Court cannot appoint a minor's parent as a sole guardian of a minor's estate. You would thus need someone else to be the guardian. You could be appointed as a co-guardian along with the other guardian.