Is it possible to create a neural network with two inputs, with sequential layers?
Sure!  There's all sorts of ways you can pass in two inputs.  Your idea of stacking the inputs like a 2-channel image is one idea.

Another possibly simpler idea would be something like this:



The intuition is that the network learns intermediate representations for the two sentences, then compares the representations.

Of course, you have an enormous amount of flexibility in how you configure the network connections. There are endless variations that allow you to have two (or more) separate inputs.  For another example, check out DeepMind's pysc2 paper.  On page 10 you can find diagrams for networks that deal with three different inputs.  There's a flat vector of non-spatial features along with two different spatial inputs.