Per this Apple document:
Apple Trade In - Apple
Apple will recycle Items not eligible for trade-in at no cost to you.
I've already looked up the numbers for the iPad 2—too old to have any trade-in value.
can I recycle them safely even if I can't get them to power up anymore for me to clear everything off of them?
iPad storage is integral with the logic board and cannot be removed.
Hopefully someone else with more iPad hardware expereice than I will step in to advise how to recycle a non-starting iPad.
2012 and older MacBook Pros have user-accessible hard drives so you can physically remove the drive from a non-starter, a perfect condition for recycling. IF the drive still works you can put it in an external enclosure or bare-drive adapter and revover data or continue to use it.