Hello!!! Montgomerys is the surname! It is not plural. We use 's to indicate belonging! I believe you already know that. It becomes different when the word or name that we are using already ends with an "s" For example with the name "James" You'd expect "James's car" or "James's shoe" but that is not correct. When indicating belonging in word or name that already ends with an "s," we simply add add the apostrophe (') at the end. We would write "James' car" or "James' shoe" Other examples: Business' income was over $2000 today Tomorrow, we're going Nicholas' house.

Montgomery is the surname of the family in whose house the person had dinner. The Montgomery's = the Montgomery's house/ home...

It is the correct way of spelling this word. I took it from their site.

It is the name of the home fashion brand in the USA that was named after the founders using their surname. In this sentence, it is regarded as a shop. Some more examples: McDonald’s, Macy’s, Sotheby’s, Christie’s, Children’s Place, BJ’s Wholesale Club, Sam’s Club, Carabba’s Italian Grill, Moe’s Southwestern Grill

The Montgomerys is a place like a public house or something of that nature!