I am the cake wallet dev that added silent payments, currently I only work on the Bitcoin features and other misc changes around the app, and the web services, while another dev is focused on evm coins like ETH, SOL and TRX, and another dev is focused on the Monero stuff, etc there's more and we are all able to work together as well

we use common libraries for everything in the code, the bitcoin features are added on top of the https://github.com/mrtnetwork/bitcoin_base dart library which allows more people to have eyes on it since libraries can be reused by any other codebase

pretty easy to do actually, and with this productivity stack this gives us room to have features other wallets don't have (like silent payments) and we can research for more, like paynyms, payjoin, coinjoins, etc, which is what I am doing, I do this while the bitcoin wallet is working and doesn't need to be changing all the time, and the other devs are working on the other stuff, then always moving a few steps ahead