Both the word "Lares" and the word "Penates" are plural - the Lars and the Penates are two groups of supernatural beings, not two gods.
The Lares (singular Lar) were household gods, geniuses of a certain place which they were supposed to watch over and care for (though some Lares were associated with particular families as a family guardian spirit).
The Penates are also household gods, but are always associated with a particular family rather than a particular place - they are supposed to be the ancestors of the family, watching over them from the afterlife.