The best way to force a sync is to press Menu → 'Sync now' on the platform on which you made the updates; then press → Sync now on all other platforms to see the changes immediately there as well. Please note- you must be in 'Task View' to do the 'Sync Now'.
If they are still not syncing, log out and back into the app on all platforms. If a shared task is not syncing, press 'Sync now' on all accounts on which the task is shared. If this is not working for you, please tell all the members to log out and back in on all platforms with their Any.do account.