welcome to spring!!they are probably more randy than usual...
firstly, it is not foolproof to sex a bird using the stance method..as a matter of fact, I'd say it's a silly way to do it and often wrong.
You won't know for sure unless you get them sexed or one drops an egg!!!
I have two lovebirds, one of whom i KNOW is a female from the eggs...the other, I am unsure of. Both feed each other, both nest, both are terribly in love with one another, both mount the other...so I'm thinking two females and since both nest and tuck stuff in their feathers (although the definite female is better at it), both are cage aggressive so I'm thinking I'm right. But I will also probably do the DNA test...
As for the on/off love-in...don't think you have to worry.....mine do the same thing every once in a while. Best buds one minute, snuggling and preening each other and then the crazy beak fight. Unless you really notice a problem, I think they are just being lovebirds.
And that beeping sound is funny, isn't it? I also call it the beeping sound.