If the household is too small for a whole lamb, they are to share with the nearest neighbor based on the number of people, and apportion the lamb accordingly.
Jewish Publication Society of America Version (JPS1917) - Exodus 12:4 >and if the household be too little for a lamb, then shall he and his neighbour next unto his house take one according to the number of the souls; according to every man's eating ye shall make your count for the lamb.