Learn Russian: Следовательно, мы говорим о двоих оценщиках. - Consequently, we are talking about two appraisers.

You can actually use either here! However, collective numerals like двое (two) and трое (three) are very frequently used with masculine nouns that denote people, such as оценщик (appraiser). Using о двоих оценщиках sounds very natural to native speakers, though о двух оценщиках is also grammatically correct.

If двое usually takes the genitive plural, why is оценщиках in the prepositional case here?

The rule where the number forces the noun into the genitive plural only applies when the number is in the nominative (or inanimate accusative) case. When the sentence requires an oblique case—like the prepositional case here, triggered by the preposition о—the number and the noun must agree. Therefore, both simply take the prepositional plural: о двоих оценщиках.

What declension pattern does двое follow to become двоих?

In oblique cases, the collective numerals двое and трое decline exactly like plural soft-stem adjectives (such as синие). The prepositional plural ending for these adjectives is -их, which gives us the form двоих.

Is there a difference between using следовательно and поэтому in this sentence?