Dedicated graphics card (eg, GTX 940M, really anything is an improvement on intel) and a reasonably powerful CPU will work on all sims games. The games you'll have the most trouble running without dedicated gfx are TS2 (compatibility) and TS3.
FreeSO runs on intel but it could certainly run faster (VRAM thrashing causes stutter), currently the bottleneck is usually the cpu generating the sprite geometry.