You can only use the internet plan on one device at a time, but you can use the internet on both devices yes. You'll just need to log in and out of devices as you wish to use the internet.
If you think there would be a need to use the internet on both devices at the same time, then you'd need to buy two internet plans.
You can use the Hub app for free, no need to purchase an Internet plan, on any number of devices. I do recommend installing the Hub app before you get onboard.