Adding an additional family member to a tenancy

General Discussion

The current tenants of my 2 bed flat have been reliable tenants for the past 8 years. The tenants are brothers, originally from Cuba but have Spanish passports and have been in the UK long enough to qualify for UK residency. The tenants have recently emailed me to ask for their mother to be added to the tenancy agreement, as she needs to be registered for Council Tax in order to continue to access hospital care. Apparently, their mother came over for a visit last year before the pandemic started and owing to these circumstances she had been unable to return and they have now decided that they want to care for her in this country. They have apparently applied for and been granted right to remain for their mother, prior to Brexit.

As I mentioned, they have been good tenants who pay the rent on time, however, I am a little annoyed that they are only contacting me now they want something in asking me to add their mother to the tenancy agreement, rather than asking me if it is okay whether she can continue to use the residence as her permanent address. Legally, I believe that they had an obligation to tell me that an additional adult was now residing at the property, as soon as they realised that this was likely to be a permanent arrangement - presumably they had a pretty good idea in December 2020 when they applied for the right to residency.

My questions for the forum are: should I just be glad that their staying at the property and looking after their mother there rather than looking for a larger property?
Should I be worried that there will be 3 adults living in a 2 bedroom first floor maisonette?
If the paperwork for the mother’s right to residency checks out and she passes the Landlord right to residency checks, are they any other issues that I should be thinking about?

At the end of the day, the whole point of a tenancy agreement is that additional tenants aren’t added to the property without agreement from the Landlord. Obviously, I appreciate that the situation with the pandemic was unforeseen and their clumsily worded email is probably a result of being slightly ‘lost in translation’ - rather than asking if it is possible, they say they ‘might need my help’.
They sent the email request on Wednesday, they are chasing me for a response by text at 9.30pm on a Friday night. Last year when I renewed the tenancy, it took several weeks of chasing to get the returned signed tenancy agreement.

I’m just taking time to think through all the options, before I reply to their request. I want to make a fair and reasonable decision, especially under difficult circumstances, but also to make the point that they should have asked permission around six months ago.

Any advice welcome, thanks.