These are all done digitally with pen pressure for varying line thicknesses. You could absolutely get the same results with a dip pen and or brush pen. There are many resources available to learn how to ink and how to control the varying thickness and if you are interested I recommend Arthur L. Guptill's: Rendering in Pen and Ink for traditional inking methods and techniques (though do note the book is older and some of the business advise/materials mentioned have become obsolete but it still has some good material).