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Good morning welcome to just answer. I am a solicitor and I have reviewed your question for you.
There is really no visa for a visa national to come and assist a person that is subject to immigration control in the UK. They would need to apply for a visitor's visa which will give them 6 months and hopefully the assistance will not require them to stay longer than the 6 months as the visitor visa can not be extended from within the UK. If you were a child who was British and needed a parent to come to look after you or you were a parent and the person coming was a child thne dependant visa wold be an option.
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