The correct answer is: between.
The preposition “between” is used to indicate the relationship between two or more things. In this case, the speaker is dividing his property between his two sons. This means that he is giving each son an equal share of his property.
The other prepositions in the question could also be used in certain contexts. For example, the preposition “among” could be used to indicate that the speaker is dividing his property among a group of people, not just his two sons. The preposition “in” could be used to indicate that the speaker is dividing his property into two or more parts. The preposition “of” could be used to indicate that the speaker is giving each son a portion of his property.
However, in the context of this question, the preposition “between” is the most appropriate choice. This is because the speaker is dividing his property between two specific people, his two sons.