Maybe their parents happened to excel in different types of abilities, and their daughters reflected that by inheriting one or the other? Hilda with her battle proficiency, and Yolda with her transferal powers. It's also interesting to note that Yolda holds the same type of devotion to En that Hilda has towards Beel. They might have been raised for the very purpose of being wet nurses/surrogate mothers. If I remember correctly Hilda comes from a very esteemed family, so it might be a clan/traditional thing or something to that effect.
Was nice to see an entire chapter devoted to Hilda, always a pleasure to see her knock around some fools with her superlative demonic strength. Oga's rubbing off on her, how cute.