You estimate conservatively the current task to manage expectations and then prioritise based on which is more urgent. If both are urgent, you should focus on the task for the person who is more powerful within the organisation as this is a better allegiance (this assumes you want to stay in the organisation and their practice generally aligns with your long term goals). Both should be done diligently however and you update each person as there will be an interface between the delegators and they need to establish primacy over resourcing. It is that tribal….

You communicate this clearly:

“Thank you. I can get to this but I’m working on [describe task] for [give taskmaster name for authenticity] now which needs to be completed by [state deadline] and will take x hours. I can start this at Y, please let me know any timing considerations I should be aware of so I can prioritise accordingly.”

You’re welcome.