How do you apply a multi qubit gate to specific qubits in a multi qubit circuit?
Imagine that the qubits were $0$ and $1$ (or $1$ and $2$, depending on your numbering scheme). You want to apply the Hadamard gate on the first two coordinates, and nothing – the identity – on the rest. This leads to a block diagonal matrix whose second block is the $4\times 4$ identity.

Now make the necessary arrangements for the qubits you're interesting it.