It would be more correct to pronounce the surnames Сергачёв and Фёдоров as Sergachöv and Födorov. In Russian there is a letter "ë", which after a consonant sounds something like "ö" in Swedish. And sometimes, to transliterate a surname from Cyrillic to Latin, the letter “ё” is transferred as “e”, and sometimes as “yo”. The fact is that the Russian language does not have a unified Latin alphabet, so the same word can be transliterated in different ways. But for convenience, you can imagine that there is "ö". Sergachöv, Födorov, Kovalöv, Sömin, etc.