See if you can alternately take each for a run every week or so would be my advice. The rubber bits (hoses, tyres, seals) benefit from being used regularly, as in getting it all up to working temps, or they go hard and brittle.
I’ve had multiple cars that were used sporadically in the past and the only stuff I ever did to them was to keep the batteries topped up (removed if storing for 3 weeks or more) and rotate the tyres (prevents a flat spot developing) if they were standing for more than a month.
At one point I had a winter and summer car with the other one being stored in a garage on wheel stands with a trickle charger attached and a window open to stop it getting musty inside. Once a month I’d run the engine for a bit to stop anything seizing, more applicable to the winter cars as they were bangers.