Can I replace "marriage to someone" with "marriage with someone"?

Why would she mention "game" here?

She mentions "game" metaphorically! The phrase "game on" here is commonly used when means a competition is about to or has just started. She uses it because she's excited about the heist! While it is serious, it is also cool and fun. Ex: A: First person to prank Jake wins. B: Game on. Ex: It's game on with this criminal. He's not getting away.

Why does she use "That’s definitely not", why not "That’s not definitely"? (I'm curious about the location of "not")

Great question. She is using "definitely not" to emphasize that she was not expecting what her sister said. So it is emphasising her certainty that her sister would say anything apart from that. "Not definitely" would mean you're not certain about something. So it gives the opposite feeling. Ex: A. Are you going to the party? B. I'm definitely not going. This means that B is certain they will not go to the party. Ex: A. Are you going to the party? B. I'm not definitely going. This means B may or may not go to the party. They are still undecided.

What does "long way round"? Is it round trip ticket?

"Long way round" means to take a longer route to your destination than taking the direct route. It doesn't necessarily mean a ticket. Another way to say "long way round" is "scenic route;" taking the longer route instead of a direct route. You will hear "scenic route" in American English than you will hear "long way round." Ex: Let's take the long way round. I'm in no hurry. Ex: I'm taking the long way round to Colorado. I want to take my time. Thank you so much for your question!

What does "fist bump" suggest?

A 'fist bump' is a gesture similar to a handshake and is usually used between two friends. It often suggests friendship, and can be used as a way to greet someone, congratulate someone, or show approval.

What's the "dark web?"

The "dark web" refers to the part of the World Wide Web (the Internet) that isn't available through search engines and can only be accessed through special software or browsers. People use the dark web use to make sure their activity remains anonymous or untraceable, like criminals or spies. Ex: You can find a lot of creepy, scary stuff on the dark web. Ex: The dark web can often be a haven for criminals hiding from police.