Do they use cold wallets for it like everyone else? If so, do they keep everything in one wallet or do they split the bitcoin into several different wallets?
Let's say 1/3 in Trezor, 1/3 in Ledger, 1/3 in BitBox02? I'm currently trying to transfer my bitcoin from an exchange to a cold wallet for the first time, but I'm wondering if it's safe to keep everything in one wallet from one company.
It would be safer if you split it into different wallet, regardless if its hardware or coldware, as long as you keep them safe and private all their seed phrases. Storing all your assets in just a single wallet is more risky, once your account is hack or stolen, all your assets will be lost too. It’s like diversifying your investments into crypto, stocks or bonds, the more you diversify, the more secure your profits are. As long as you never go wrong into putting all your investments profits, it will always be safe and secured.