Two siblings na student were asked to manage two local FB pages

Two siblings na student were asked to manage two local FB pages for an online shopping store and one Messenger GC (Admin) to answer customer queries.

They agreed to do the job in equal effort to cover one person's shift. For 6k php per month. The prob starts now, the owner is now expecting them to respond 24/7 and wanting a work for two to be done, knowing that they are only going to pay for one.

Pwede po mag ask pano gagawing approach sa owner? Thanks in advance!