Mods Adding Multiplayer?None functional. Engine not designed for netcode. The Sims 4 has limited multiplayer via mods (Sims 4 Multiplayer Mod), but not TS2.
If You Want Social Sims
The Sims 4 (Base Free): Gallery (share/download), but still single-player. Multiplayer mod exists (alpha).
Second Life / IMVU / Avakin Life: True multiplayer virtual worlds.
Stardew Valley (Co-op): 4-player farming/life sim.
TS2 is a solitary experience. That's by design — and many prefer it that way.