My advice is to take care of your interest (finishing your studies in the deadline that is important to you) while in the same time trying not to completely destroy the relationship you've built with your advisor and supervisor. How to do that? Well that depends on the specifics of your contextual situation.
1. Do you have enough material to start writing your thesis? If the answer is YES then start writing and start sending drafts of your chapters to your supervisor. They will anyhow need time to read and review them so include their time in your plan! (Also, plan additional time for revisions in your provisional time table!) If, on the other hand, the answer to this question is NO then first write a draft of the thesis. Maybe it's required by your university, maybe not but it will help you. In it include what you already know and don't yet know but anticipate - possible research questions, methodology and the data that you have. If possible include the hypothesis or/and conceptual framework and possible outcomes of your research (obviously adapt and expand this according to your scientific background, area, field...). And ask for their comments. In any case start writing - it's your job to write your thesis and it's important for you to dive into it as soon as possible because it is just not possible to see all potential obstacles or challenges before you even begin to write.
2. While they are busy with reading and reviewing your drafts you will be waiting and will very probably have time to do your work on the research. These wholes are also the time that you could use to do that additional work they are asking from you. I hope that work is at least somehow important for your own research - if that's the case with time you'll see how much of it you can really do, and how much you just can't.
If at some point you notice that it is all being dragged for far too long, take a more firm approach and start asking for more frequent in person consultations. Come with ready questions and suggestions.
This is going to be a very stressful and busy period but as you said you have plans and they seem very legitimate to me.
Hope I helped. Hope others will add their advice as well
Good luck 🤞🏻