Storm in a Teacup of Misery

Here's a tricky task for you, Fork. Solve it instead of doing repairs.
Matvey Grishin's one of the twin daughters fell ill. In the process of treatment and tests, it turned out that he is not the genetic father of the girls. But this just can't be! The shocked man excludes infidelity on the part of his wife: Verusya and Natusya are two copies of him: dark-skinned, dark-haired, brown-eyed... Grishin asks Viola to investigate this matter and clarify everything.
His head is spinning from these twins! Fork and Stepan started digging skeletons out of the closets of the strange family and stumbled upon... Matvey's double, a certain Boris Bogdanov. And just when the mystery was about to be solved — Boris is found dead. The case takes a very serious turn.