Swaping Properties

I am in the process of purchasing a new house. I have looked at many options and narrowed down on a house in the same locality few meters away for which discussions are underway and almost a done deal (H-A). I am also interested in my neighbours house with which our house has a common wall so that I can connect the two houses into a larger one (H-B). (All these house are same dimensions) I have expressed an interest to my neighbour to purchase H-B and suggested that the neighbours take H-A as replacement. They understand that H-B is convenient for us and are charging a premium amount for doing so. Based on the above arrangements please advise: Q1. How will the transactions flow? Sequence wise - should I conclude my transaction first or his or parallelly? Q2. Regarding payments - Should I be making any payments to the owner of H-A instead of the neighbour? If he says that I directly pay to the owner of H-A (asking price of H-A) and just the balance (premium amount) to him. Q3. What contractual agreements should I enter into with my neighbour and the owner of H-A? Q4. Both the owner of H-A and my neighbour wanted part payment in cash and part through wire transfer. Should I be paying it to the owner of H-A the cash portion on behalf of my neighbour. What proof should I ask for in lieu of this amount. And what assurance should I take from my neighbour? A clean transaction for me would be to just deal with my neighbour and let him deal with his own thing. However I am anticipating that these issues would arise if the neighbour takes advantage of my situation for his own convenience. Please suggest me how to approach this.