Yes, someone with a Power of attorney can indeed act on behalf of the party for whom it is issued and "step in to the shoes" of the property owner if need be.  But the Power of Attorney that you have does not seem to cover the ability to do what you will need to do here unless it a signatory transaction (which I guess bringing an action for ejectment or trespass could fall under by a stretch as you are "signing" court papers but I really think that it is a stretch and not what the power of attorney really is referring to).  So I would go and have your brother execute a new power of attorney to allow you to act on his behalf here.  You can use a general power of attorney "for all legal purposes" or be specific.  I would go with the general.  Good luck.