Sims 3 & 4 on same computer?

Both games will be fine on that system. You will want/need to arrange for frame rate (fps) capping for TS3 if you haven't already done so or planned to do so because, being an older game, it has no functional built-in fps limiter and your graphics card is strong enough to throw wildly high frame rates if left unchecked. TS4 has this function built in so nothing to worry about there.

I or someone else here can expand on those instructions if needed.