Is it possible to remember all of our past lives?
I have never heard of anyone able to do this, except of the Buddha, who it is said remembered all of his past lives when he fully Awakened. Some texts say he remembered 500 of them, others report that he remembered several thousand past lives. It is known that as one progresses on the spiritual path, a side effect is having siddhas or powers that can take the form of telepathy, psychic powers, materialization of objects, etc. It is possible that one of these siddhas would be to see past lives. All great saints and sages have advised not to pay attention to them, as they are a distraction from the true path, and can reinforce the ego, if one is not careful. Therefore we may never know how many people have actually seen all of their past lives. I don't think trying to think about our past lives in this way would be helpful, as the information could be overwhelming and confusing for most of us.
However, I receive letters from people that can remember either part of a past life, or one or several in vivid detail. As our past lives are stored in our subconscious, it's possible that some of these memories surface as visions or dreams in those people that have "thinner veils" to the subconscious. I suspect that most of the time these memories surface because there is something from the past that is unresolved and still has a deep effect on that person's emotional being. It is also possible that some memories can surface randomly. One can measure the importance of such a past life memory, vision or dream, by the emotional feeling that accompanies it.
The Buddhists have a chant or prayer asking one be forgiven for all past life deeds that were harmful or destructive and to be released from the effects that these deeds have caused. Yet, they don't focus on past life therapy as a means of healing. I think, though, that the intention to heal the past through asking for forgiveness is something that we can all incorporate in our daily lives, even though we may not remember any of our actions from past lives. Having this kind of intention is beneficial as we can also apply it to letting go - forgiving ourselves, and forgiving others more easily in our present lives. When we forgive and let go, we feel much more expansive and compassionate, and we have more available attention to be directly present in the moment. Our minds become more calm and stable, which allows for more contentment, and for deeper meditative states.