Should I do handover of tools and methodologies I have developed?
Yes, I'm afraid you do need to hand over all work product that you created while employed. You were part of a team and if you try to subvert the team by withholding things that arise from your employment on the team you are trying to blackmail them into keeping you employed. I smell a lawsuit here. 

But you should cooperate fully just as a way to boost your own future career. How do you want to be spoken of in this field? Do you hope that people will want to collaborate with you in the future? What value will your tools have if no one wants to come near you in the future. 

And without you or your contribution, the team will find someone who can provide an equivalent service. You may feel indispensable, but you are not. 

Sorry to be so harsh.