A ház"ba" sounds very strange to me with érkeznek. Is it really correct? èrkeznek a házban (in the house) seems right to me.
:D The sentence is correct. Those new people are coming from outside into the house if putting it like this helps you.
"At" seems to mean that they do not come IN . How would you translate then "a hazhoz"?
"Arrive at" might mean that they come in, since English is pretty imprecise with its directions. "Érkezik a házhoz" would translate to "arrive at the house" just the same.