There are instances in which a 1st person inclusive plural shows by its morphological structure that it consists of the 1st person plus the 2nd person, e.g. Tok Pisin ‘yimi’, but I have found no instances of a dual inclusive formed in this manner.
Standardized
Pronouns for 1st person inclusive plural may consist of 1st person plus 2nd person [singular] forms, but pronouns for 1st person inclusive dual may not.
Kriol (a language spoken by some thousands of Aborigines across the north of Australia), where the inclusive dual consists of 1st and 2nd person forms, but the inclusive plural not. (McGregor 1989: 445)
Implicational version:IF a 1st person inclusive pronoun consists of 1st person +2nd person morphemes, THEN it is inclusive plural, never inclusive dual.
Implicational version:IF a 1st person inclusive pronoun consists of 1st person +2nd person morphemes, THEN it is inclusive plural, never inclusive dual.