In بَيْتًا فِيهِ كَلْبٌ وَلَا تَصَاوِيرُ, فِيهِ consists of فِي (“in”) and ـهِ (“it”). The pronoun refers back to بَيْتًا, the house.
The terms كَلْبٌ and تَصَاوِيرُ describe what is present there. وَلَا connects the second mention to the negative description.
For comparison, بَيْتٌ فِيهِ كِتَابٌ means “a house containing a book.” The comparison illustrates how a pronoun refers back to a preceding noun.