Q: Dharma is not constant. It may be changing according to the Time, Space and Context of the Role of the Person in question at that moment. One size does not fit all.
A: Yes Dharma is best expressed as right action that is the result of awakening the inner Intelligence. It cannot be figured out through our limited knowledge as that only results in confusion. This awakening requires purification, inquiry and total surrender of the false individual self.
Q: In the suggestions for Purification, it is mentioned - leaving the home, seeking solitude and sadhana, with company of seekers. Is it not possible to be a seeker, go through the purification process, within the world, if one is constantly practicing like what Lord Krishna has spoken of in Bhagavad Gita - primarily do the action without any expectations of the result. Secondly, I think, (this will automatically.bring the first) practice doing everything with a conscious attitude of offering to the divine. Seeking solitude to do 'Sadhana' is one suggested for one who has actually fulfilled and completed his duties and roles in the world. Our Ashrama system has prescribed Vanaprashthanam at a stage of physical life, only after certain prerequisite conditions of the person in question has fulfilled. Otherwise there is a danger of one running away from one's dharma, under the false notion of 'Seeking' the true knowledge. - my two cents.
A: Leaving the home for retreats is not to shirk any responsibilities prematurely. It's best to engage in the world and discharge whatever we have to do and make our actions sacred by offering them to the Divine and be equipoised toward whatever outcome is ordained. But one can still take retreats either in solitude or in the company of other seekers to whatever time possible. Taking a week off from the regular routine of life to be alone can be of great help to look inwardly, read, meditate etc in an immersive way. Or whatever time one can afford to take off periodically.
Q: Is purification done through the dropping of thoughts?
A: It is the dropping of the thinker. Can't be through volition but inquiry. Purification is also removing impediments to true inquiry.