Wasalam
The answer for Teespring and Reduble is all above. If Merch follows the simple principle as these two then same ruling will be applicable.
I have not looked at Etsy unfortunately.
Ideally, they all need to be reviewed properly again in more details.
For dropservcing please see the following link: Is Drop Servicing Halal? - #2 by Mufti_Billal
Kind regards