Yes, you may, but you must be female. After that, make them a vassal. Then they're no different from any other lord you may marry. Even the female companions, strangely, because they are treated as if they are masculine themselves. It is possible to marry both your male and female companions simultaneously.
There are some problems with this approach, though. First of all, it is exclusive: you can marry only one companion at a time. Also, there's no way for the companions to improve their status - once you marry them, they stay that way forever. Finally, there's no way for the companions to inherit your lands or titles.
In conclusion, marrying your companions in The Banner Men isn't recommended.
You are unable to do so. Because the mods that allow you to marry companions (even ennobled ones) as a man are open source, they cannot be included in a paid DLC like Viking Conquest. You may marry a female friend as a female, but that's about it. There is no other way to marry a companion.
That said, there are some mods that allow you to marry your friends even if they aren't women. One such mod is called "Comrade". It adds a new relationship option - comrade. To match with this option, go to settings screen and select "Relationships" tab. Here you will see a new section called "Matching Options". In here you can choose what kind of matches you want to make (e.g. romance, friendship, or comrades). Comrades are best friends who can also have romantic feelings for each other. They will appear in your party as normal characters and can help out in fights - they're not helpless like wives are. However, comrades can't be married nor can they inherit gold. They're pretty cheap to keep around though - 500 gold per year.
So yes, you can marry your friends. But only certain friends - women friends and comrades. Other kinds of friends cannot be married.
You can't do it. When you try to use the coercion option "I'll reign with him" on the land, he will inform you that people will not accept a Circle Mage as Queen, and that if you make him King, he will bump you after the land. If you are a female human noble, you can only marry him and become Queen-consort. Otherwise, the kingdom will not accept it.
In Skyrim, you can marry anyone, regardless of gender or race. You can even marry a dark elf if you want to.
Dark elves are one of the playable races in the Elder Scrolls series. They can be chosen as your character's race at the beginning of the game, and they will receive experience points for doing things such as killing monsters or completing quests. If you choose not to breed with a dark elf woman, she will eventually leave the city to find marriageable men elsewhere.
Like other races, you can marry a dark elf to gain benefits. For example, you could marry a dark elf to avoid having children with another race. Or you could marry a dark elf female to have access to her special abilities later in life. There are no restrictions on marrying dark elves; their appearance or race is not important. What matters is that you like them enough to want to marry them!
Marrying someone from another race in Skyrim does not require permission from that person's family nor does it cost gold. However, certain marriages may give players advantages in relationships with other characters. For example, if you marry a human woman, she will stop wanting to sleep with other men once she gets pregnant.
Female human nobles who are romantically interested can arrange to marry Alistair outright; if they are not in a romance, they can enter into a political marriage. Either option necessitates Alistair's permission and leads in his becoming king. If the female human chooses not to marry or become queen, she retains her status as a noble and may continue to hold titles. She cannot, however, vote on royal affairs or act as a monarch.
The only humans who can marry him are female human nobles who are romantically interested or married women whose husbands are alive and well. He cannot marry a goddess, an angel, a demon, or a ghost because all these species are immortal.
Alistair can have many wives and husbands. The number of marriages he enters into is irrelevant since he can divorce any wife at any time. The nobility often arranges marriages for their sons and daughters to avoid having too many young people living together out of sight. These matches may not be romantic but they help families build their kingdoms. Divorce is common among the nobility because it is easier to arrange another marriage than to deal with the complications of a broken one.
In some cases, two female human nobles may choose to marry each other instead of marrying Alistair. They would need King Edward's approval to do so but it is possible.