Looking to Upgrade My 2017 DDR3 PC: Suggestions Needed

I've recently started using my PC from 2017 again and I'm considering a few upgrades. My brother has a spare 8GB GPU I could swap for my current 3GB one. I want to enhance my setup a bit, but I'm wondering if there are additional upgrades worth considering. The power supply seems sufficient based on the calculations, and I'm thinking about replacing my 2x4GB RAM with 2x8GB sticks. Is it even worth trying to run both GPUs together? My storage of a 250GB SSD is fine for now. I don't play many heavy games—mostly casual stuff—but I'd like to manage at least 20 FPS on E33 at low settings. If not, I might just play it on my brother's PC instead.