You can do them in pencil, but you won't be able to submit the homework for paid critique if that's what you want to do.

Getting critique may be more difficult ( as previously noted ) but if that's all you have then don't let that stop you doing the exercises. Follow the guidance though ie don't erase or correct. Treat it as if it was ink.

Hello! You can use a technical pencil, but there are a bit less convinient (according to my experience) because those pen have been made to drawn a lot of fine straight line and are mainly use in comics (for box border and action lines) and architectural drawing.

So technical pens are very useful in lesson 1 for drawing the boxes and the table but may be less in the smooth line exercice. A black ball pen works well too. Uncomfortable chose black fine liner because 1) they are relatively cheap 2) you can't erase a line after doing it 3) black because it is best on white printing cheat. Feel free to post exercices made with black ball pen and then when sending for review, made the exerciced with the fine liner. Make sure to but several because you never know when the ink will run out of the tip damages. Good luck