The feud between the Johnsons and the Davids, two families each with a deep-seeded hatred for the other, is a well-known story in the whole city.

Correct sentence - The feud between the Johnsons and the Davids, two families each with a deep-seated hatred for the other, is a well-known story in the whole city.

The phrase "deep-seated" refers to something (such as a belief, feeling, idea, or behavior) that is deeply ingrained in something else. The phrase "deep-seeded" may sound like it makes sense, at least from a metaphorical point of view, but the phrase is incorrect.

After turning right onto Royal Street, walk five more blocks and then turn left onto Main Street?

Correct answer - After turning right onto Royal Street, walk five more blocks and then turn left onto Main Street.

The sentence is imperative and should be punctuated with a period and not with a question mark.

Brendan always said he only needed two things to be happy and healthy. friends and family.

Correct sentence - Brendan always said he only needed two things to be happy and healthy: friends and family.

A period is used to end a sentence, but a period after "happy and healthy" may suggest the sentence has ended without explanation. A colon is used instead when introducing an explanation, example, or list. This will maintain the sentence’s flow and clarify the direct connection between the statement and the mention of "friends and family."

Health experts advise people to limit their consumption of sweet foods because of high levels of fat sugar and cholesterol.

Correct sentence - Health experts advise people to limit their consumption of sweet foods because of high levels of fat, sugar, and cholesterol.

In this sentence, the items in a series are part of the dependent clause. The word "because" signals that the rest of the sentence after it relies upon the preceding part of the sentence. Used correctly, the commas here separate fat, sugar, and cholesterol into three distinct items.