Thanks for your question. I will try to help.
I am a Practicing Immigration solicitor in England and Wales.
Unfortunately, because you have obtained indefinite leave to remain after your children have become adults they are not entitled to register as UK citizens.
Additionally, because of their age they are also not entitled to obtain a Visa on the basis of their relationship to you as their mother.
They are for all intents and purposes treated the same as any other foreign nationals whose parents do not have links to the United Kingdom. The only possible way that they might be able to obtain a Visa on the basis of your relationship would be if one or both of them were dependant on you to the extent that they can not carry out personal/household tasks in their home country because of illness or disability. They would also have to show that the care they need is not available in their home country and that you would be able to support/accommodate them without claiming public funds.
So, provided they are independent adults capable of looking after themselves and working in their home country they would not quality for this Visa which is called an Adult Dependent Relative Visa.
I assume that they would wish to work in the UK but they do not have access to £200,000 for investment in UK business and are not world leaders in their employment fields. On this basis, the most relevant Visa that they can apply for is a Tier Two Sponsored Skilled Work Visa., which is a work visa sponsored by a UK employer for a job they would do in the Uk.
They would have to secure a job offer from a UK employer who is or would become a licensed sponsor of skilled migrants:-
You will have to see if there is a job that they could do in the UK on the shortage occupation list:-
If their job is not on this list then this means that their employer would have to apply to become a licensed sponsor of skilled migrants and also confirm to the home office that they have carried out a the Resident Labour Market Test. This test is effectively to show that their are no resident/eea national in the locality that can perform the role,.
I am sorry that I could not have better news for you.
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