You have highlighted two issues, carbonation and head retention.
On carbonation, if you have sufficient yeast in the beer at packaging time (usually anything above almost clear is enough), if the carbing is carried out above about 18*C, then two weeks should be long enough for all of the priming sugar to be consumed. I use PET bottles and PBs and know that most of my beers have carbed up within a week at the most. So the only thing left is the quantity of sugar used. I suggest you use this
https://www.brewersfriend.com/beer-priming-calculator/
Next there is, in my opinion, no need to use anything other than table sugar for priming. It is readily available, cheap, predictable and can be easily and accurately measured out. Conversely carbonation drops are the opposite, so my advice is don't use them.
And as you use a bottling bucket and add sugar solution, my suggestion is to put the solution in first then add the beer to get better mixing.
On head retention brewers often add speciality grains to improve this, including, for example, torrified wheat. If you are all grain then you can add these grains easily, but if kit brewing there is not a lot you can do other than add these grains via a steep or through a small mash. Finally if you leave your beer to condition longer this might improve head retention, something to do with smaller bubble size I have read on here.
PS
+1 on
@Clint comment about clean glasses. If you can see tiny bubbles on the wall of your glass when there is beer in it, your glass is not clean.