Undefined tenancy period in agreement

Have entered into an agreement (about 10 points) with the friend of a friend to rent a new self-contained building next to the main house.

We (owners and tenant) came up with a rental agreement of our own that both parties (owners and tenant) agreed to and said the same by email.

At a 3-month review meeting, the owners gave the tenant very early notice that they may place the property on the market in several months time (due to a recent change in the owners circumstances). The tenant had previously asked to be kept informed early of any tenancy issues such as this….the tenant was upset by this news (naturally), and insisted a 12-month initial term had been verbally agreed at the outset. The owners dispute this in fact only one of them was present for this discussion with the tenant which only alluded to the possibility of 12 months, but was never clarified.

The email agreement initially referred to does not mention a lease period, ..and  the tenant did not ask for this to to be modified after review to include such a period of 12 months.

Still no action (sales contract ..etc) has been taken by the owners to sell the property in question (now 4 months into the tenancy)……

The owners are trying to reasonable here…hence the very early heads-up notice, this in itself has caused tenant distress…not intended.

Ethical and legal feedback welcome….this is the owners first foray into renting out a property or part thereof.

ps this has caused a certain ongoing tension between the parties since the 3-month meeting….

pps the tenant has been given a 40-50% discount on the rental cost which  amounts to about $100 / week discount. This discount was due to being part of an organisation to which we are all connected ……

Are we being reasonable in expecting that the tenant may have to move on in the last 3 months or so of the perceived 12 months???