Read the following scenario:

John is living in the basement suite of a house that is owned by Chris, his best friend. Chris has $2$ tenants living in the house $($David upstairs and John downstairs$).$ Chris, a licenced realtor by profession, decides that it is time to sell the house and sends out a letter to both John and David asking them if they are interested in buying the house before he puts it on the market. In the letter, Chris explains that he is "interested in selling his house" and he'd be "willing to take $$500,000"$ but that he'd only wait for $7$ days to hear from either John or David.

A few days after John and David received Chris' letter, Chris decided to advertise on his website that the house was for sale. Seeing the ad$,$ John wrote a letter to Chris offering $$500,000$ for the house and mailed the letter before the promised week was up$.$ John expected to hear from Chris as soon as he received the letter with his offer but had to leave town immediately due to a family emergency. John tried to call Chris but he was unable to connect with him.

David called Chris the day he put the ad up on his website. During their conversation, David offered Chris $$455,000$ for the house. Chris never had any intention of selling the house to David as he felt that David was a bad tenant. He only gave David a copy of the letter he sent to John as a courtesy. Chris also knew that David sold cannabis on the side and that this was David's main source of income. Instead of making any commitment one way or the other, Chris just told David that he'd "think about it$"$ and said that he'd get back to him.

Chris received John's letter $8$ days after Chris sent his offer letter to John and David. A day prior to receiving John's letter, Chris accepted an offer of $$520,000$ for his house from a man called Spencer. Spencer saw the ad on Chris' website and contacted him via email. Spencer was looking to buy a house in the area as an investment. He lives in England and has no intention of moving to Canada. Although Spencer has the money, he is $85$ years old and suffers from dementia. His estate is governed by a trustee who is legally entrusted with making all financial decisions for him.

Explain, using the principles of contract law, the position of each of the parties involved in this scenario.