sul sul 
I’m actually working on such since few years ^^ a bit further than sims to build villages and cities, but for social interactions, house building, house holding it is pretty similar.
For your question, both can do it, which is easier depends on your experience and goals. With Unity you can buy a lot systems/plugins you might get to work together, but without having deep control and knowledge about these it can quickly cause a lot problems.
With goals i mean features, scale/performance and target platforms. With THREE you might notice a lot needs to be done by yourself (but you probably won’t be satisfied what is offered in the store of Unity and need to do it yourself too there) it is more of a highly flexible render engine.
But i need to say that your information given is a bit too less and the question too unspecific yet. As i said it also depends on what you’re more experienced with, if you started with both it likely will be hard anyway, such a game with all required systems and networking is a lot work and complex.