Heavy bullshit. Extremely similar languages - yes. Same - no. And no - Croats don't have serbian ancestors...that's just some more of world famous serbian propaganda all over again.
As for Google language tool - that's correct - it doesn't really recognize subtle differences. It often offers me suggestion that something is in "bosnian" when it's in croatian and vice versa. Same goes with serbian... So ,results here are definitively misleading.
They sound similar because it's same language, but different dialect. Serbs in Bosnia, Belgrade and Montenegro speaks the same language, but with different dialect.
Yes, Croats, at least 85% of them have Serbian ancestors. That is visible on almost every step in their country, but pressure of Catholic Church was brutal and many Serbs were forced to declare themselves as Croats. So, basically they were told to my people: ,,From now on you are Croat, you speak Croatian language and you are Catholic".