Don't mean to be the dissenter of the group. . . but. . .
A few questions : Are the proteins cut approx. the same size? If they are, or at least slices of pork and chicken @ 1/8 - 1/4" thk, it will stir fry in the same time the shrimp will. Cooking time is irrelevant.
Are you using a wok at very high temp? If you are, then the "nasties" aren't a problem at all.
As far as taste. What cuts of pork and chicken? I assume you are using chicken breast and probably chops?
I personally don't find it to be a problem marinating all together.
For how long? 30 minutes or 8 hours? What is the marinade? Are you using the marinade as an ingredient additive in the stir fry? Is there either fish sauce or oyster sauce being used? Soy? Dried shrimp or shrimp paste? If the sauce is going to cover all proteins, any homogenization of flavors during the marinade won't matter much, especially if you are using shellfish based sauces. The difference between eating shrimp and pork should be unmistakable, especially in texture, but depends on the cut. Chicken breast usually assumes the flavors of the stronger ingredients in stir fry's or is mild, unless you are using chicken fat somewhere in the preparation. Using fish based sauces or condiments is very common, so the cross flavorization (Is that a word?) occurs all the time. i.e. eating pork with a "fishy" sauce or ingredient. You would think a fish ball in a soup with roasted pork would overwhelm, but it doesn't.
The only problem I see is for shellfish allergies. However, if this is a "Chinese cooking at home" recipe book, then I'm guessing anybody with allergies would simply omit the shellfish. A commercial kitchen would be something else entirely - should be separated