Hello armssh,
If I'm understanding you right, changes you make to Stocks on your Mac aren't syncing to your iPad and iPhone. I have some steps you can try that might help resolve this.
First make sure that you're signed in with the same Apple ID on all of your devices and Stocks is enabled for iCloud. On your iPhone and iPad this can be in Settings > [your name] > iCloud. On your Mac, go to System Preferences > Apple ID > iCloud. If you make a change to your watchlist on your iPhone does it sync to your iPad (and vice versa)? Test it out if you're able to as this helps narrow things down a bit.
Next, restart your iOS devices and your Mac and then test to see if Stocks is syncing now. Update your iPhone and iPad if they aren't running the most current iOS versions available: Update your iPhone, iPad, or iPod touch. Also install any updates available for the macOS version you're running: How to update the software on your Mac. Test things out once again. If changes made in Stocks seem to be syncing between your iOS devices but still aren't syncing with your Mac, turn off Socks in iCloud on your Mac. When prompted, select "Keep on My Mac". Turn on stocks again and select the option to "Merge" when prompted this time.
Thanks for using Apple Support Communities. Respond back if you need continued support with this.
Take care.