Let's take Froome first.
Froome and Thomas are now in the twilights of their careers and although they still have the ability to turn it on at times, their best days are now behind them.
There comes a time when they have to move on, think Kevin Davies for instance, great player for us but simply kept in the team in the end more through sentiment than current performance and when the manager at the time eventually did what was right for the team at the expense of the player, it was him seen as the villain and not him doing the inevitable.
Froome and Thomas simply didn't deserve their places on the team when it was named and a gamble was made in bringing in Carapaz that didn't work out as they hoped it might. Froome and Thomas both have very good chances in their respective Tours to come and hopefully Froome will end on a high with Sky/Ineos before he takes his final big pay day contract with the Israel team and hopefully gets them established as a pro team for years to come.
Thomas is still under contract and is a very good team player so he would have no problems being part of Sky again but it isn't unheard of for teams to release cyclists still under contract to enable them to join other teams.
I don't know what will happen, I guess it will all boil down to money as usual - would Sky want to get his huge wage of the payroll in the Covid era and if so what other team would pay him what he wants as they are in the Covid era too!
There is a transfer window in cycling but it is more to do with riders moving to other teams at the end of their contracts rather than big money transfers as in football.
To be honest I've never been bothered much with the team race and how it is worked out.
I would have thought the same as you in that the first (say) four riders in each teams their points/time are added up and at the end of the race whoever's points/time is the lowest of all the teams win.
It doesn't necessarily follow that the GC winners team also wins the Team race, depends I guess on how many sacrifice themselves and finish way down on time in order to help their leader do well in GC.
I've found this that list the team results for last years TdF where Sky finish first and second with Bernal and Thomas but only came second as a team!
To be Fair though the team that came top is the team of Alaphilippe who led the race for most of it, Bora, the team that finished fourth had both Sagan and the rider who finished fourth overall in the Tour and the team that finished fifth had the third place rider.
The team that finished third though is a bit harder to work out why though? They had Nibali who was up there near the top before he crashed out but other than that most have had a solid team throughout I guess?
Sorry, I can't be too helpful on this one!
https://www.procyclingstats.com/race/tour-de-france/2019/startlist/teams-rankedhttps://www.cyclingnews.com/races/tour-de-france-2019/Hope your mum in law is ok and of course should be your first priority.
Maybe you can start to get her hooked on cycling now!!!
Sorry, forgot to answer another point you raised.
Sometimes the team plan changes to who is the best positioned rider on the Tour at the time. What I mean is that last year it could be argued that Thomas, who was team leader, should have won the Tour but events took a turn when one of the later stages was stopped before the end giving his team mate who was ahead on the road at that particular time the deciding advantage to win the Tour instead.
It's not uncommon to go into a race with two or even more team leaders and let the 'road' decide which of them to eventually all get behind.
This of course can and does lead to many internal team upsets and squabbles - and probably best to be avoided if you can.
Froome was the best rider when Wiggins won but played it straight as per his contract as being there to help Wiggins to win. The deal was the next year Wiggins was to stand aside and let Froome win but Wiggins went back on the arrangement and cause no end of problems for all concerned.
Thomas and Froome are examples of good team players with talent, Wiggins and Quintana bad team players with talent.
Up to the management to do the right thing because trying to please everyone doesn't always work.
Sky/ineos plan this Tour was to have Bernal as the leader and Carapaz as plan B but Carapaz wasn't ready in time for the race and lost too much time early on to be a viable alternative and meant Bernal was his top man down on helping him retain the title.
From what's happened since Carapaz seems to be a good team player with talent but I'm not fully convinced Bernal is - time will tell if I'm right or wrong about that.
Hope that gives you a better perspective on this issue - hope so anyway.