Please lend a ear. I keep 6 hives at home (South Africa - scutellata).
1) The bees in one of my hives are much more aggressive than the others - they go easy on the attack. Is there a way I can rectify that behavior by replacing the queen? We cannot buy any queens here. All my swarms are from removals.
2) In another hive of mine the bees cover the front of the hive almost every afternoon - almost like a traffic jam to get in, yet its not that. They have sufficient space inside and I even supered up to make sure it is not that - I don't use excluders either. They are not in direct sunlight either. It is an old treated hive so I don't think its smell either. They don't seemed bothered by their behavior either. They havn't smarmed while showing this behavior.
3) How do I use mint plant to discourage verroa mite?
>1) The bees in one of my hives are much more aggressive than the others...
I have no experience with pure scutella, but from my exerience with European honey bees, I'd say you'll often get a calmer hive by simply disposing of the current queen and letting them raise a new one. You can also use queen rearing techniques (another subject) to raise queens from your calmer hives to requeen the hotter ones.
>2) In another hive of mine the bees cover the front of the hive almost every afternoon...
Usually this is resolved by increasing the ventilation. Some kind of top vent will probably help. Prop the top open perhaps? Are these in Langstroth hives? Top bar hives? British standard hives? If it's basically a vertical hive (boxes stacked on top of one another) then I'd just prop the top open with a stick and see if it resolves the problem. If so you can either leave it at that or make some kind of fancier top vent. If you search on this site for "ventilation" you'll find many discussions on various solutions to ventilation problems.
>3) How do I use mint plant to discourage verroa mite?
As far as I know, you can't. Some have used essential oils (which are very concentrated extracts) from various plants with moderate sucess, but my guess is your best bet is to make sure you use either no foundation or small cell foundation and you shouldn't have too big of a Varroa problem. Most Scutella are on 4.8mm foundation or no foundation and this works fine for controling Varroa. If you put them on the enlarged 5.4mm or 5.5mm typical foundation for European bees they will crash from the Varroa.