Illegal Informal Settlers (squatter) on our Lot

Hello po Attorney(s) and good day to you all. My aunt owns a Residential Lot that she was able to purchase in the mid 1980s. She managed to marry a foreign national, and stayed abroad since then. Upon leaving the country, no structure has ever been built upon the lot, not even a perimeter fence, and because of this, and without anybody supervising the lot, few years ago, she leaned that the lot has been, unfortunately, occupied by some Illegal Settlers (squatters). How to resolve this? Who can help us? Can the City Hall do something about this? Who shall evict them? We hold all original documents to prove she is indeed the Lot's owner. Thank you very much! Mabuhay kayo!