If I’m understanding you correctly, then if I wanted every node in a layer to have 4 inputs, I could just do something like:
def forward(self, x1, x2, x3, x4):
    x = x1 + x2 + x3 + x4
    x = F.relu(self.fc(x))

And each input (x1 … x4) would be given its own weight parameter?