Is there an API that can be use to create a decentralized wallet

Please, is there a Trusted and reliable API that I can use to create a decentralized wallet?
Where my users can:

  1. Generate their Wallet Addresses that will have a private key and 12 secret phrase
  2. Can receive and send Crypto Coins and tokens
  3. and Work on different networks Just like Trustwallet

Using an API wouldnโ€™t make it very decentralized. Hereโ€™s one I found to create wallets.

For points 2 and 3, you will still need some sort of interface or app for users anyway, like MetaMask.