I was involved in a matter several years ago, in which the deceased made a specific devise of the property in which they resided at the time of their death. The circumstances of the property in which they lived at the relevant time were much the same – a flat and garage under separate Land Registry titles.
Counsel’s advice was sought, and the question came down to whether the garage was used as a part of the residence – i.e. did the deceased use it for their car or otherwise as an extension of the flat (e.g. storing possessions which might otherwise be put up in the loft). In that instance, a neighbour was allowed to use the garage and counsel advised that it fell outside of the gift.
I suggest that, when considering if how the garage in the case now raised should be dealt with, the first step is to consider the circumstances as at the date of the brother-in-law’s death. Whilst this might not be determinative, it may well help inform the decision.