You can’t force WordPress to use iOS emoji for anyone but iOS (or Mac) users.
Emoji are just characters, like any other letter, and how they’re displayed is determined by the operating system. Each operating system has its own graphics for the emoji, and they will be displayed using these.
However, to enable emoji in browsers and operating systems that don’t support them WordPress uses a script to convert emoji to a backwards-compatible format, and these backwards-compatible emoji are Twemoji, Twitter’s emoji designs. It uses these because they’re open source, which is a requirement for WordPress.
You can disable these backwards-compatibility emoji with a plugin like Disable Emojis. When using this plugin emoji will only appear in compatible browsers (most of them these days), but they will appear in the original style of the user’s operating system. So iOS users will see the iOS designs, but Android users will see their device manufacturer’s designs.
It’s not possible to force everyone to use Apple’s designs for emoji, because these are copyrighted and tightly controlled by Apple.