As described in the linked post, the functional API calls would be dropped.
In your case this flatten operation 26 would be missing.
Your error is raised, since model.modules() will recursively return all modules. You can check it via print(model.modules()).
model.children() would yield the submodules in their order of initialization.
However, even using this approach would assign the first nn.Sequential module (called .features in the original VGG16 model) to model_stimuli and model_target and will thus still raise the shape mismatch error.
Due to these shortcomings, I would thus only recommend to use nn.Sequential for very simple modules and not try to wrap other models inside it without checking the definition of the pretrained model first.