Can anyone suggest a good non-custodial wallet for XRP and TRX .
You may go with brain wallet for XRP and TRX. I started using brain wallet for staking purposes and it has been more 2 years and I am not facing any issues with them. All you need is, securing your seeds for backing up your wallet. They support all major coins hence you may find all your need with brain wallet in most cases.
What if I want to manage ETH separately, how will I do that ?
Do you mean separate wallet for ethereum alone? I use that way. I use MEW mobile app for ETH and we can link to desktop for convince time to time when transacting.