First, convert the mixed fractions into improper fractions:
\[
4 \frac{1}{2} = \frac{9}{2}, \quad 6 \frac{3}{4} = \frac{27}{4}, \quad 7 \frac{1}{5} = \frac{36}{5}.
\]
Now, find the greatest common divisor (GCD) of \( \frac{9}{2}, \frac{27}{4}, \frac{36}{5} \). To do this, find the GCD of the numerators and the LCM of the denominators. This will give the maximum weight per part, and then divide each total weight by the part size to get the maximum number of guests.