Tom is the tallest and the most intelligent between the three siblings.

"between" is used for comparing two entities, while "among" is used for comparisons involving more than two entities. Since the sentence involves three siblings, "among" is the correct preposition. "the more intelligent" is not appropriate in the context of making a superlative comparison. For a superlative degree, "the most intelligent" is the correct form. The other options either use the wrong preposition or have incorrect forms of the adjectives. Therefore, "Tom is the tallest and the most intelligent among the three siblings" correctly and clearly expresses the intended comparison.