I start by saying, your customer who uses an iPhone is never going to use an Android, and vice versa, so there is no need to keep them consistent and identical looks and design wise. You should use the native items as much as possible because a random user is more likely to understand the common system version than they will understand your bespoke version. Use the native share icon, don't use the iOS share icon on Android, etc.

Also iOS tends to be way more consistent than android, windows, etc, so there could be a case for iOS native and 'company consistent' for everything else, especially if you're in the USA. iOS people pay more and it could be worth it to have two branches for customer support if it leads to total better conversions and thus more profits. Your business's core competency is not making UI toolkits, it's selling whatever your making. Leverage the literal billions of dollars apple and google invest into the core UX toolkits.