Siebe,
Can you see that you are equating ‘we’ with Nibbana deep down?
In Nibbana, there is no longer any ‘we’, in the sense of clinging to an identity view. Of course, arahants and Buddhas still talk about themselves, but they no longer think of themselves as having any true selves. It is the clinging to self-identity that prevents us from attaining Nibbana. A living being would have to give up any conception of ‘itself’ in order to attain Nibbana, and to cease dukkha, unsatisfactoriness and suffering.
You are falling into language traps, which condition us to think of ourselves as being a definite agent and being. Yet ultimate reality is nothing like that.
Even the question ‘How is this possible when anything about us would be unstable?’ assumes a stable self that needs to be saved, and after saving, still retains the characteristics of a self or being.
But in reality, we are just a collection of physical and mental processes conditioned by avijja and tanha, blinded by self-identification, and desperately and unknowingly trying to keep the cycle going on and on forever, despite a nagging feeling that there is dukkha in it, and that we would suffer unhappiness, disappointment, pain and disillusionment, yet thinking that there is no other way but to continue on, grasping against all odds at mundane, worldly happiness that can never be permanent.
You also wrote: We will never be able to make a refuge of ourselves, if, in deepest sense, we would only be unstable mental and phyiscal processes. I do not understand why this is not clear.
‘We’ cannot make a refuge of ourselves, if by ‘we’ you mean dukkha and sansara. Nibbana is the only ultimate refuge, but The Buddha, Dhamma and Sangha serve as good temporary refuges for us before we attain Nibbana.