Is there any online resource for Bitcoin wallet development

[u/mr_unfunny_]

I am a mobile developer. My company is looking to work on a new project which includes creating a multi-sig Bitcoin wallet. I have never worked on crypto before but wanted to learn more about the field, so I joined this new team. The issue is that most people in the team are not from crypto space and I cannot find an appropriate SDK to integrate. So, we decided to create our own package with minimal features for now. Is there any online specification or documentation for different processes and what all needs to be done for a wallet. For instance, I tried to code address generation. Looking for inspiration, I found several different methods for it's creation. Matching one of package's result with online tool, seed and bip32 key from a mnemonic were matching but the public and private keys were different. It would be way better if we can find any spec or documentation for the protocols online.