Yes, to simplify, the mnemonic key/seed phrase is the master key of all of your cryptocurrencies. All the cryptocurrencies private keys are derived from your mnemonic key.
If you want to use a separate ETH address, you can simply generate a new address, the new address will simply be generated based on the mnemonic and the wallet itself will do the job in the back end.
Thanks for clarification, so what non-custodial wallet are available for above mentioned cryptos , definitely I want to avoid likes of Atomic or Exodus . Don't we have something like Electrum for these cryptos ?
Yes, there are exists other light clients for those cryptocurrencies like Electrum. But I don't specifically know much about XRP and TRX. So I guess I will leave that to others. Regarding Ethereum, Metamask is the most majorly used wallet, and it is also full opensource. Anyway, I believe that if you want to maximize your security, using a hardware wallet is a no-brainer, just make sure you use HW that supports multi-coin.