This is not how you open an app on Mac; you use NSWorkspace to launch other apps. For a web page, you generally would never launch Safari directly though. That would create multiple instances of Safari, which is not generally what users expect.
If you want Safari to open an URL in its own window, bring that window to the foreground, and place that window at a specific location, you'd generally use Apple Events. For example, the following AppleScript will open a 1024x768 window at location 100,100 for example.com:
tell application "Safari"
open location "https://google.com"
set bounds of first window to {100, 100, 1024, 768}
end tell
The easiest way to run AppleScript inside an app is with NSAppleScript:
let script = NSAppleScript(source: "...")!
var error: NSDictionary?
script.executeAndReturnError(&error)
if let error = error { ... error handling ... }
AppleScript is a subtle and tricky language, and often poorly documented. You may need to experiment a bit to make sure it's behaving exactly as you want. But it's extremely powerful and the core technology for controling other apps.