I don't know what kind of shrubs they are but if they are the only large plants in the area and they have been around at least 15 years, the roots are probably coming from them. I think I would take them out anyway. As a rule of thumb the roots grow upside down from the canopy. the roots will spead as wide as the spread of the natural canopy but most roots will be in the top 3 ft of soil. If the plant has a tap root and it has not had water and the sewer was the closest water, it would have reached out for it. It is best not to plant any large plants within 10 feet of any utility unless you know how invasive the roots can be.
Happy gardening in Hawaii. Gardens are where people grow.