Love requires a certain level of equal standing between the partners that is not possible in either situation you suggested. You can’t really love a dog in the same way you love a person, and a dog definitely can’t love you in the way another person can.
But two women or two men can love each other. And many do. And in a world filled with hate and senseless violence, real love should be celebrated in all its forms.
If these couples are copulating on the dance floor, by all means, skip the wedding. But I have yet to attend any wedding that celebrated sex. They celebrate love.
And love is not a sin.
(keep in mind that you don’t know for sure what goes on behind closed doors, maybe they plan to live chastely together. who knows?

)
(And P.S > the Catholic Church is fine with middle aged men marrying 14 year old girls. So your last example is a little on the fence … I personally would say no that’s disgusting … the church apparently is basically OK with it.)