1kg seems about right.. an iphone X is 174 grams, 2 is 348g, plus add the packaging and you'd near 1kg.
I really hope this ends good for you, because honestly I'd be really concerned. I'm going to go into lawyer-mode for a second so bare with me. You have no way of proving that the phones weren't in the package. Once you picked it up from the depot, they will say you could have went around the corner, took the phones out, repackaged it, and started a complaint that the phones were missing. This is an eBay scam that's been used for years.
The only thing I can think of is that Apple can blacklist the phones. However, I don't know if they will give you replacement phones. If the packaging was upside down, someone through the process clearly opened the package and re-packaged it after taking the phones.