Hi Ashley,
A basic phone video (maybe with graphics or subtitles) could help you with this problem.. In the past we've found videos recorded with a mobile phone (held on Landscape) and supplied to our Guests prior to Arrival can help them with Entry/Exit arrangments. Video can be supplied to them Privately and naturally no sensitive code material is shown in the vidoe.
The beauty of this is that your Guests are made conscious that there is an Entry/Exit system that is differenent than the normal and this is clear in their minds before Arrival. This system could help instead of having a kind of information overload scenario.. Another thing to rememeber upon Arrival.
A 2nd key store is fine as long as you take in mind that all previous Guests who have been shown the 2nd set of keys, could, technially access your property again...
All the Best,
Cian