How can i add a 2nd homey pro for my vacation home in the app?
Yes with this : Introducing HomeyLink – News | Homey
You can add a second Homey Pro in the app by opening the More tab and selecting your current Homey. Afterwards, you will see a list of Homeys where you can click “Add Homey” and add a 2nd Homey Pro to the app
Depends if it’s connected to internet?
If true, an advice:
A cold reboot, or a PtP, can be a challenge when the vacation home is unoccupied (Murphy’s law).
Just add a smart socket between Homey’s power unit and wall socket, which can be operated from anywhere, independent from Homey. Like Shelly devices.
You can’t really use Homey without internet connection, at least setup will fail and you need to be connected to the Athom servers once in a while (AFAIK every 14 days) when it needs to refresh the token for use with the mobile app. Also web app is unavailable, and the only devices that will work are devices that are directly connected to Homey and the Flows need to be setup with an internet connection.
I know all that, Sven 
The TS didn’t post any info about it, hence my remark. Folks seem to believe (the ads) Homey can run without internet.
