I wouldn't worry too much about this now, sounds like the govt hashed out... something before Christmas that clarifies the position a bit better. Whoever is here before the cut off date in March 2019 or otherwise decided will be fine under the "old rules" and they aren't going to kick anyone out.
Nothing is agreed until everything is agreed – so if there is no agreement the offer also falls away. If there is no trade deal then the UK will decide who will be able to stay and on what terms that will be. The UK is not a stranger to ending free movement as this was why the Immigration Act 1971 was created, to end Commonwealth citizen's type of free movement to the UK. This is the same law the UK still uses today for immigration.
Even if there is a trade deal and that agreement holds, you will see from reading that EU citizens offer that there will a percentage who will not be allowed to remain in the UK. As there are millions in the UK who entered under EEA Regulations or European Court of Justice Rulings, that will likely be thousands. And as also clearly pointed out in that agreement for EEA citizens and agreed by the EU, the UK can remove any law in Parliament at a later date if they don't like it as that is how UK laws work.
Nor will the UK have to "
kick anyone out" as the UK now has the Immigration Acts 2014 and 2016 for those not lawfully in the UK. No renting, no working, no bill free NHS, no benefits, no driving, their UK driving licence revoked, their bank accounts closed and frozen. Some of these have now been made a criminal offence with jail time under that 2016 Act.
However, Mechlady's husband is highly skilled and I doubt they will have any problems, no matter what happens.