I've got a question when conducting a path analysis.

I've used one sample group and created three different path analysis models (which are mostly identical, except for one mediator.)

To make my questions clear, the three models are illustrated below:

1)

a---> b1--->c (dependent variable=continuous)

2)

a---> b2--->c

3)

a---> b3--->c

Now, my question is, after running the the 3 models respectively, how can I test the significance of the differences in coefficients of b1-->c, b2-->c, and b3-->c?

Many thanks in advance.

best,

Clara