Fortnite requires at least a 2.4ghz i3 so your x3 will have very low IPC to be able to play it at any decent frame rates no matter what you upgrade (aside from a new cpu / mobo / ram)
Overwatch, playable since you are at minimum depending on your GPU (at least GTX 460 or Radeon HD 4850)
CS:GO should not be any problem, and any GPU with DX 9-compatible with support for Pixel Shader 3.0
What's your budget to upgrade?
If you just need a graphics card, the best entry-level bang-per-buck would be the
Radeon RX 570 for $120 ($140 w/ $20 MIR), and you can always move it to your new system - speaking of which, the below system would work out out as a decent starting point for your core system upgrade, and would even play them pretty well with the on-board GPU.
PCPartPicker Part List:
https://pcpartpicker.com/list/PLP7QZ
CPU: AMD - Ryzen 3 2200G 3.5 GHz Quad-Core Processor ($84.99 @ Newegg)
Motherboard: Gigabyte - B450M DS3H Micro ATX AM4 Motherboard ($66.89 @ OutletPC)
Memory: Corsair - Vengeance LPX 8 GB (2 x 4 GB) DDR4-3000 Memory ($47.99 @ Newegg)
Storage: Kingston - A400 120 GB 2.5" Solid State Drive ($19.99 @ Amazon)
Power Supply: SeaSonic - S12III 450 W 80+ Bronze Certified ATX Power Supply ($31.98 @ Newegg)
Total: $251.84
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2019-05-07 11:23 EDT-0400
You could upgrade the memory on your existing system, but not sure that would be a good investment considering how low-performing the CPU is these days. Would be great for a poor college student or someone's kids if you sold it on the cheap to fund your new parts.