The only reason to change the name of civil marriage to civil union is to deny some group the use of the word "marriage". Since it won't be the gays who are you proposing to restrict marriage from?
Under the law, the word "marriage" should not exist.
In the current form, allowing marriage between 2 people but not allowing marriage between 5 people is a clear case of religious discrimination. Religion A's form of marriage is allowed, but religion B's form of marriage is not. Drop all of it. No form of marriage should be officially recognized by the government. There should only be civil unions. You can still get married in a church, but you would be signing a civil union contract at the end.
Think of it like a Jewish bat mitzvah or a Christian girl's sweet 16 party. Does the government officially recognize either of these celebrations? Nope, but they're still celebrated. Straight people can still get married by a church and invite all of their friends, but their religious ceremony would not be recognized by the government.
You realize people have been getting married in some form for 4,000 to 5,000 years the practice predates Christianity.
If you're a true fan of history, you would know that modern day marriage is nothing like traditional marriage. Women were literally property. A "marriage" was the act of taking ownership of a woman. This is why a woman's father walks down the aisle with her and hands her over to the man. In India, women are worth less than property. When you sell a car, which direction does the money flow? The person releasing the car receives the money. How does marriage in India work? The parents of the daughter
pay for another man to take her. She actually has a negative monetary value.
In the bible, women are frequently mentioned as if they are property. Do you know what the punishment is for raping a woman? Pay a fine to
her father and then marry the woman. It's basically a "you broke, you bought it" rule. I imagine the rules for slaves were very similar. If you kill my slave, you owe me some money to buy a new one.