I wonder what type of brushes you are using.
I have never had problems with curling on natural hair or bristle brushes.
I frequently have issues with nylon bristle brushes.
The cheapest brushes are natural pig bristle which is an off white colour and very stiff.
Cheap children's brushes use very soft natural animal hair which is dark brown or black.
Artists brushes for acrylic paint are often nylon or sable.
Sable is dark brown natural hair and reasonably stiff and usually expensive.
Nylon brushes are often yellow or pure white and very even in thickness as every bristle is the identical diameter.
With Nylon brushes, you can reduce the curling by avoiding painting abrasive surfaces.
If you put sand on bases, drybrushing the sand will quickly destroy the tip of a nylon brush.
I actually use pig bristle brushes for drybrushing sand.
The second curling problem is due to dry paint near to the ferule.
This can be avoided by cleaning the brushes after every painting session with soap.
If you have dead brushes, that are stiff with paint or have splayed bristles it is worth trying to clean them with decorators paint thinners.
You can often resurrect a dead brush with a good clean.
Dip the brush in thinners and roll it over kitchen paper to work the paint out of the ferule area.
Practice this first with a brush that you would throw away.
Then you will learn just how rough you can be without breaking the hairs - it is more than you think.