If you copy the package to the cloud as well and give it appropriate permissions (either by making it Public or using PermissionsGroups or individual access via the Access GUI or ...) include the following in your cloud notebook instead of <<MyPackage`:
Get[CloudObject["user:<yourusername>/<path>/<to>/<yourpackage>"]]
(you can also give the full URI if there might be doubt about what $CloudBase will get used when the file is downloaded -- this will work on desktop as well)
As long as the user you've shared the notebook with has permissions to the package CloudObject, they will be able to use the code.
