Twins can appear identical but never the less one may be in doubts. In any case they are siblings and siblings can look quite similar.
You can get the answer with DNA testing. I send you two test kits which you post in the enclosed envelope. They are handled anonymously without any information about the names of the siblings. After a while (usually 1 – 2 months) you get the answer, a written certificate on paper showing the relationship.
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