The second is correct. The first one works...but I think the grammar is wrong. I'm having trouble coming up with a similar sentence to compare it to. I think the "who" ends up being an extra subject in the second clause. But I can't seem to reconstruct the sentence in a better way, with that structure. I would probably rewrite it: There is a person who might or might not be my brother.

If someone gets a patent on a specific protein, they are given exclusive rights to that protein. They are the only ones allowed to make or sell that protein. This means that no one else can work with that protein, which takes away their freedom (liberty). For anyone that wants to work with proteins, allowing people to patent them costs them their freedom to work with whatever proteins they want. And that cost is true for everyone who allows the intellectual property rights to be enforced. However, the number of people who want to work with the proteins is small, so the total cost (in liberty) may be small.

I think it is a mixed conditional. It's a bit weird because narration often uses the past tense to refer to things that are actively happening in the narrative. "I ran down the hall, and climbed the stairs. I saw him standing there." But yes, the if clause is in the past, and the conditional clause refers to a possible future.

They are all correct. I think you would only use #3 if you were already talking about expanding a social circle: If you feel lonely, you might try expanding your social circle. One suggestion is to get a pet. A pet helps you with expanding your social circle. Every time I say it, though, I want to change it to "A pet can help you with expanding your social circle".

Fortune means destiny or luck. At some point, people started using it to mean wealth, possibly because they were fortunate==lucky. Fate and destiny mostly have the same meaning. Fate is sometimes viewed as an active force (the Greeks had creatures called "The Fates" in their religion), choosing the path your life takes. It can also refer to how you die. Destiny is more often used to refer to a fixed point in your life, that is decided, sometimes by "fate" or some other mystical force. So if you said "He went to the store and met his fate there", that probably means he died. If you said "He went to the store and met his destiny there", that probably means he found his purpose in life. But, again, they basically mean the same thing, and you can almost always use them interchangeably. I can't quite understand your "torment" question. Torment means to cause pain or annoy. So I suppose Vikings can torment their enemies by raiding their villages. I admit I've never heard it that way, though.

Katherine is her first name. Black is her last name. "C" is her "middle initial" -- the first letter of her middle name. You would probably call her Katherine, based on this information. However: 1) She may go by a shorter version like Kathy, Katie, Kate, or Kat. 2) She may go by her middle name (formal documents will often show first, middle initial, last, but that doesn't tell you how she refers to herself). 3) She may actually go by a totally different nickname, which you would have to learn. 4) If your relationship is formal, you might use her title and her last name (Miss Black, Doctor Black, Professor Black). 5) Bonus answer: In sports (and probably other settings), people often refer to each other by last name. Then you might say, "Black, run down the field"

stead is a somewhat old word that means "standing or place". You find it in older phrases like the one you mentioned, and in compound words: homestead (can mean home or the land), instead (in place of)... there are others. You'll see it in some town names, as well.