Is there any formula to determine the physical properties of a
resultant product after the combination (mixtured or dissolved) of two
organic sustances.

In particular the surface tension, electrical permittivity and resistivity.

At the very least is there a 'boundary condition', ie. the resultant
product cannot have these physical properties greater or less than the
either of the individual components.

In the absence of specific interactions such as complexation or
hydrogen bonding, the properties of mixtures are pretty close to
proportional contributions of components.
If A is mixed w/ B in proportions x/y, then the property I of the
mixture would be: I(A+B) = I(A)*x/(x+y) + I(B)*y/(x+y).