Destruction of Info on iPhones and iPads
Memory is not the place where information is stored. Yes, the info is what we want to remove from these devices, or at least make the info unrecoverable. Info is stored on a hard drive (a spinning drive or SSD -solid state drive), not in memory. Memory, also known as RAM (random access memory) does not store any info, it is simply the place where software does its work, and the more you have, the faster the device can do its work (a faster computing device).
So, drilling holes in the information storing part will make the recovery of the info exceedingly difficult (a tough task even for the CIA and such types). But, drilling also introduces the danger of fire if the battery is cut open. Lithium battery fires produce toxic by-products and are difficult to put out (check with your fire department).
A more expensive option is a machine designed to safely crush and cut up the whole electronic device producing scrap.
The removal of information from these devices could be done with software that would overwrite the info with meaningless or random characters. The software may have already been written by the device manufacturer. They may have also produced connectors to pair the devices with the overwriting software installed on your service computer. Stay safe.