Budgie Health Questions and Concerns

First thing I want to say is hello to everybody and a thanks towards this forum as I've been here before many times and learned quite a lot of things about budgies, as well identifying a health problem for one of my budgies.

As I am a 3 months new budgie owner, I have some questions regarding some behaviors and health issues that may still be present with my budgies.
I have 4 budgies, two males and two females. One of my female has been brought to me by my grandpa and at the time when he gave it to me I only had one male and female that are kind of a couple.(They still work on their relationship ). My family told me to give her away, but I love pets and animals so much that in a couple of minutes I've became attached to her and I couldn't give her away. I brought her a partner and I was forced to buy as well a cage for her and her new partner to live in.

The hen that has been brought to me by my grandpa is sometimes aggressive, and I was forced to buy a new cage for her and her new partner because of this, because I don't know why she was always picking a fight with the other male budgie that was not her partner and as well had a big fight with the other hen, where I was forced to intervene to stop them
My first male budgie is named TLB(The Little Buddy), he has a face of an innocent, is so calm and harmless that its like a little baby angel :budgie:
And because of that he was always crying and running when the aggressive hen was attacking him (her name is Furiosa, go figure). So I had to move her with the new male budgie (Snowflake) in the new bought cage only for them. Surprisingly enough she is not attacking Snowflake as long as he doesn't stay in her way and Snowflake always sings to her and to my surprise she even kisses him when he flirts with her, but the moment he does something wrong she tries to peck him

And here comes my first question. Why is Furiosa like this? I've searched through here and on internet and by the answers that I've found I think it may be some hormonal problems, I also think she is the oldest of the bunch because she has full brown cere and I say that she may have hormonal problems because she has a little crust on her cere, and I'm pretty sure it is not mites or anything as the crust is not big and is brown as her nose color.
But I'm asking if maybe she has a health issue because I've read on internet that sometimes when budgie are aggressive they might have some health issues. I want to mention that she is active as a normal budgie would be, eats well (even fruits), drinks well and is full of energy when she is flying. But I'm asking of her well being because when Snowflake approaches her and he doesn't try to kiss her she attacks him. (I also put her back in cage with TLB to see how she reacts towards him, but I am getting the same answer, she still attacks him, although not as bad as before).

And my second question is for Snowflake and the other hen, called Bella (Bellatrix). I don't know why but both Snowflake and Bella, when they get tired they breath so heavily and I can hear something like a click in their chest when they breath after they fly too much and get tired. Is this something to be worried for, because a friend of mine has a budgie for almost 3 years now and sometimes when his budgie gets tired I can hear this clicking sound in him too. I want to mention that I hear this sound only when I hold them in my hands after they fly.
And regarding the cold feet. Bella has her feet almost and always kind of cold, but again she is very active, eats well, drinks well and doesn't give any signs of sickness, it may be like this because she is paying so much attention to everything that happens around her and she may be stressed? (Although she was the first budgie that I've got of the bunch, and she most of the times now stays relaxed and with her feather fluffed, not the sick stance though. I also want to mention that for a few days now, Bella gets tired a little faster than she did before when she flies. She was flying like an airplane on turbo before and now she flies like an ''almost running out of fuel'' airplane and getting tired a lot more faster. Why?

Sorry for the long post. I've read some FAQs here and some other things regarding the behavior and health issues, but I want owners with experience to tell me what might be the problems. And maybe you may ask why I'm not taking them to a vet, all I have to say is that I don't have any bird vet around where I live and I even had to say to one of the vets here what medicine he should give to one of my budgies when he had mites. (I identified his mites in an early stage by reading this forum, so thanks again to all, and he is fine now )