I think Stirling castle is better than Edinburgh castle
Everyone I speak to who has done both agrees Stirling Castle is better and I think cheaper! I could quite happily fill a fortnight in Scotland without setting foot in a castle. Similarly I’m not really a zoo person but you might find the Safari Park better than the Zoo – although not sure how either are handling Covid.
If you do a day in Falkirk then the Kelpies are nice for a walk but not a lot to do (there is a good park for younger kids) and the Falkirk wheel is worth a visit.
On any nice day the kelpies are heaving. I don’t really get it – those people aren’t all marvelling at Andy Scott’s sculptural skills nor the engineering challenge of how they are made. If big sculptural landscaping is your thing then worth considering Jupiter Artland – but its not free. If you just want to see/do them then popping on way to/from Stirling (or even Glasgow) direction is perfectly sensible.
If your kids are teenagers and you need something active to entertain them then the chainwalk at Elie is good – check the tides! Go Ape at Aberfoyle and Ratho Climbing Centre are alternative ways of entertaining them – but will cost real money!
From Linlithgow you are about 2.5 hrs to Glencoe, 3 hrs to the cairngorms, people do drive that as a day trip just to see the view but that’s a lot of sitting in a car. If you actually are capable of walking in the mountains there’s good stuff in half the travel time which can provide a full day out. If you feel like sitting in the car to be very touristy then I guess you should probably “do” Loch Lomond. Its just over an hour to Balloch. Frankly it is over-rated. Something like Ben An on a nice day gives a better view with none of the busy over priced tourist tat!
Nearer Linlithgow Beecraigs is a great wee compact trail centre if you’re allowed out on bike, and nearby Cairnpapple an interesting wee historical diversion…
and there’s another one along a Falkirk – Callendar Trails, perhaps not quite as wide a range of abilities/technical stuff but there is bike hire there which there isn’t at Beecraigs if you aren’t bringing a bike but get the urge!
Are there things that the missus, kids particularly like doing?
Hire just eat bikes?
in the forth valley you can get e-bikes if you want to try them for novelty factor.