1. Dear Kushal, I regret to say that there are no exceptional cases allowed for individuals who have been studying abroad, when it comes to computing the period you have been abroad. You will have to come back to the UK and live in the UK for the necessary year and then apply for citizenship. It will not be possible to apply if you have been abroad for a long period of time studying.
2. In relation to your second question, if you have a British employer and you have to travel abroad for work, then days spend abroad working do not constitute days out of the UK for citizenship purposes. However, the travel must definitely be for work reasons and for a Uk employer. The preferable situation would be if you could work in the UK for a year and apply for citizenship. It avoids the difficulties of proof involving in showing you were abroad for work purposes.
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4. I regret to say it makes no difference that your brother is a UK citizen. That does not help you one iota. These are the rules and you must comply with the rules. There aren't any derogations. You simply have to comply.