Yes — you can make 2L by combining two 1L C-41 kits, as long as they are from the same manufacturer and intended to be mixed the same way.

Use roughly twice the initial water amount, then add the chemistry components in the exact order given by the instructions. For each solution, fully mix both Part A portions before moving to Part B, then fully mix both Part B portions before moving on, and so forth. After all components are dissolved, top up to a final volume of 2L.

The key caution is not to mix components out of order. The prescribed sequence helps maintain the right pH and solubility, and changing it can cause ingredients not to dissolve properly.

So in short: same brand, same kit type, correct order, and fill to 2L at the end.