I am working at the position (let's say Position 1) at a small company. Recently a co-worker from the Position 2 resigned after a few weeks of working and I was asked to do his duties.
This is a job at a different department, quite new to me, and it pays 30% more than my position. At the same time, an ex-co-worker who was in the Position 2 before the employee who quit, was able to continue working hourly as a contract worker. This is supposed to be temporarily, as this ex-co-worker will probably find another job soon (she had to resign due to relocation).
After I was asked to fill in for the Position 2, we were both working on its assignments for 2 weeks, as it was a very busy period for the firm. It was totally understandable and I did the duties at the Position 2 as my priority. When these 2 weeks were over, the director of the firm asked me to continue working the same way. He said he didn't know how long I will have to keep filling in. While the ex-coworker is available, she would teach me and do the work as well. But once she finds a job, it's not clear if they start looking for someone new fast and how long it will take (I heard it can take a month or even up to 4 months). The director said and emphasized that we have all to handle the situation like a team.
So my question is - how long is it OK to keep working at this position 2, while I am paid only for my work at the Position 1? I am looking for the balance between being a good team player and being taken advantage of. Thank you for any advice.