So my first inclination is to answer no to both those questions.
For 1, one or both the deceased persons families are involved. A ghost marriage is usually done when someone dies without a spouse. Normally the emphasis is on a man dying without a spouse, but it can also be an issue for some families if their daughter dies without a spouse.
This is a nearly 3,000 year old tradition that had a lot of nuances. In dynastic China if a woman was engaged but her fiancé died before the wedding she could still marry him and be a ghost bride for the family. It’s more common now to hear about two deceased persons.
I say that you would need consent of either groom, bride, or both because it’s almost 100% of the time the parents of the deceased seeking out a bride/groom for their dead child.
This need for dead brides has led to a bit of a body trade in parts of China were (almost always) women’s bodies are stolen to be used as ghost brides.
For 2, my inclination is also to say no. Only because traditional ideas of marriage in China (ancient and modern) still revolve around a man and a woman. That is not to say that homosexuality was non existent in ancient China, but it was framed in a different way than we see it now. It was not unheard of for men to have male lovers and be married to women. The primary purpose of marriage in China was to unite families often for political or monetary power and to produce children. It was fine to have homosexual relations as long as you did your filial duty to your family and married. If you want more information on that there’s a fantastic book called “Passions of the Cut Sleeve” by Brent Hinsch. It follows the male homosexual tradition in China, mostly because there is more supportive writings to be found about male homosexuality.
For the first question here are a couple articles about ghost marriage that I think are pretty accurate and helpful:
http://factsanddetails.com/china/cat4/sub20/entry-4332.html
Edit: I would take some articles about this with a grain of salt. Many western sources tend to write about old Chinese traditions with a very western view and don’t take culture or other things into consideration.
