I am, at first glance, inclined to agree with Christian. The property would vest with the trustees and A&B could not put it into trust or sell it. It appears that the drafter may have inadvertently created a poorly drafted condition subsequent.
However the uncertainty of the ‘decide to sell’ wording is problematical. If a decision to sell is made (is it a joint and several decision? or joint only - I would have preferred wording along the lines of … either or both… but that is off topic) in my opinion I would be inclined to treat the decision as the trigger condition irrespective of any subsequent decision to change minds.
The decision is described as a ‘decision to sell’ not an actual sale. The parties to give effect to that condition are A&B. The time limit for the decision appears to be ‘until death’. The trustees would appear to have the authority to say when the condition is met.
I agree with Bish that the condition is valid, but see below.
But what happens to the property on the death of A and/or B?
If A/B decide not to sell, say A dies, does the property pass to B entire or does A’s share go to A’s estate for the benefit of A’s beneficiaries on B’s death - the sell condition has not been triggered.
If the condition subsequent is never triggered the property must pass to A&B’s estates on the second death. What if on A’s death, B now decides to sell. The property passes to residue, B can benefit - does the will allow A’s children or estate to benefit
But is B allowed to make a sell decision on his/her own as the clause states ‘they’.
As D Holliday writes, if you can get the drafter’s notes that may clarify intention. Failing that, recourse to Counsel or court may be the only alternative. The clause is unsatisfactory and it is difficult to understand the testators instructions and rectification under s.20 AJA 1982 may be a recourse.