I just wanted to come back and say thank you again, and to report that all seemed to go extremely smoothly overnight and today. As predicted, baggage was not checked through, but it was not a problem, also as wisdom here foretold. Kids enjoyed it all as an adventure, I'm told. Plenty of logistic challenges in the days ahead, e.g. grandparents having vacated their house to allow for voluntary quarantine for everyone's safety, but those are more solveable together. We even got to watch the take-off at LHR via Big Jet TV earlier today.
While this trip will seem like child's play to many here - and I'd hope to me too on a normal day - we are not in normal times and there's a fair bit of backstory that wouldn't be mine to relay, so I am grateful for the chance to air worries, get reassurance and reset priorities. Were it not for this forum I'd perhaps not have been so confident to propose using Avios quickly and boldly. Thanks and stay well, all.