I would .. hydrate the dried mushrooms in enough near-boiling water to cover, plus a bit, for as long as you like. Lift the mushrooms out and reserve the soaking liquor. Sauté the soaked mushrooms along with the fresh
If your recipe involves a reduction stage, of wine, stock, or some other ingredient, add the liquor, and reduce alongside..
Or, if there is no step like that, add to the mushrooms at the end of the sauté step, and reduce to a tablespoon or two before proceeding with the recipe.
Take care not to add any grit or sand that may accumulate at the bottom of your soaking liquid: give the soaking mushrooms a stir or shake every now and then to coax it out, if there is any. Lift the mushrooms out rather than straining, and carefully pour the liquor off the lees, when the time comes.
As Sdarb points out in the commentary, you can measure the quantity after soaking, if you need to. That won't be exactly equivalent to the same measure of fresh mushrooms.. but if you're not wildly out, in a recipe of this kind, that shouldn't be critical. Taste as you go.