SMS messages (outside the Apple Message App system) only work on the iPhone unless you enable it on the iPhone. On the iPhone go to Settings > Messages > Text Message Forwarding. Enable your two devices there, and they should start receiving all messages that your iPhone does.
Note: Only devices using the same Apple ID / iCloud Account will show up in the list to be enabled.
Second Note: By default, iPads can only send and receive on Apple's iMessage service unless there is an iPhone associated with the account. iPad's don't have phone numbers to be sent to (a requirement of the older, universal cellphone based SMS message system). iPad's sometimes have carrier ID numbers that look exactly like phone numbers, but those numbers do not have the ability to receive or place calls. At least Verizon shows them when I look at my account.