Is the strictest manner of speaking no one can have certainty of the thoughts of others without reading their minds.

Socrates through Plato is as close as one can get, given his own lack of writing. That too suffers language and other barriers.

I don't personally see history of philosophy as primarily deriving value through perfectly accurate accounts of beliefs, but rather though exposing the range of rationals and justifications previously explored, for the benefit of ones own philosophical evaluations (or amusement).

Consider for example how early members of the academy had little consideration of the possibility of the lack of a free will, because the topics has little exposure and exploration at the time. Their writing might therefore sound less compelling to you than later philosophers.

Of course the stoics were determinists, but also compatibilists who emphasize the importance of choice.

I’m sure you would have a view on how your life should interact with other lives. I think that’s the crux of the issue here. In a world with an array of interacting life, some kind of hierarchy is inevitably created. It’s perfectly fine to say your own value of your own life is all that matters to you, but there is more going on and it’s just whether you choose to make an attempt to define some standards in that space or whether you just leave it to the individual in every case. The result could be a pedophiles life is worth living because it means something to them, which is a legitimate outcome but might have some objections!

To your first question though, it’s definitely the interpretation of the reader. As with anything, a lot of translation and interpretation has to happen. Even if you asked the men themselves, they may give you a different response at a different stage in life. It’s rare we settle on something forever!

There is only one choice. From that choice alone the illusion of freewill is born out.

Consider a simple thing like visiting an ice cream vendor and picking a flavour of ice cream. Are you actually making a free choice? Or are you in reality merely reacting in accordance to the sum of all your experiences to date? E.g. did you pick vanilla because that was what your mother always gave you? Or rum raisin because you haven't tried it yet, and your father rigorously impressed upon you the importance of trying new things? Or are you standing there lost in a daydream about the philosophical implications of the ability to be able to choose or not because of some comment you read on reddit that one time? Or are you simply unfortunate to be born in world that has mundane trivialities like choices of ice cream when you could have been lost in the endless bliss of pure love of God?

The thing about philosophy is, it doesn't tend to get you anywhere. You can speculate endlessly about anything, often with very good rational arguments that set a coherent and complete system of thought. But if it isn't grounded in reality it remains only speculation and thought. Real knowledge is realized from experience.

The point of life is to try to enjoy it as much as you can before you die.