Make sure Sync Calendar is turned on in both your Google and Samsung Accounts on both phones.
Go to phone settings>Accounts &
backup>Manage Accounts>Then tap on first your Google account, then tap on Sync account. Then make sure Calendar is toggled on.
Then press the back button twice and tap on your Samsung account. Tap on Sync account and make sure that toggle is switched on.
Do that on both phones and make sure you're signed into the same accounts on both phones. Allow a little time for synchronisation to take place then both calendars should match.