That is an interesting question. Sometimes, but not always, when we use across in English we might be saying that there is something between two objects. The school is across the street from the library. England is across the atlantic from the united states. In front of would generally mean that two objects are close. The car is in front of the house. Canada is across the river from Detroit, but it is not in front of Detroit. In front of could also mean that one object is blocking another. Sometimes the moon is in front of the sun, and so we cannot see the sun. What a profound question.

They can be, but IN FRONT means more directly opposite (delante de), while ACROSS FROM means on the opposite side with something usually in between (enfrente de).

If you're talking about two buildings they mean the same thing. But if you're talking about an object and a building then they don't. E.g. - Where's the church? - In front of the bank. (Opposite/across from the bank) E.g. - Is there a phone booth around here? - Yeah, there's one in front of the bank. (Outside the bank)