As someone who interviews, honesty never hurts, and if you really have never been in that situation just say so. (Though, honestly, I would be surprised if you had missed either of those over the course of your life.)
The purpose of the two questions is reasonably simple:
For the first, I would want to understand how you approach the problem of needing to get consensus about the solution to a problem, and how you motivate other people to solve it.
If you really don't have anything that comes close to that at work, go back to a group project you were involved in in college and talk about that instead. It isn't as good as real work - and you should tell me why - but it is a way to answer the underlying question.
For the second, I would want to understand how you handle disagreement, and especially strong disagreement, in the workplace.
Look for something where you and a colleague didn't agree about the best way to solve a problem. It doesn't have to be fancy, or super important, or angry or anything.
Talk about how you approach the disagreement: how do you find common ground, how do you handle someone who is passionate (but wrong) about their approach, how do you compromise?
Again, if you really don't have an experience like that in work, go back to college, or that time you volunteered to coach the softball team and someone told you how to do it better, or whatever.
The goal is to try and understand how you will approach those situations if you work for this company. Think about how, if you asked someone that, they could make their actions clear to you.
(As an aside, talking about - and asking about - concrete incidents, not just hypotheticals is a sign of a good interview, because what you did rather than what you think you would do is a better indicator of the next time around.)