Implementation of IIR Filter in dsPIC 33EP - Scaling
The tf2sos function takes an input filter of order 
$N$, given by $H(z)=\frac{\sum_i^{N} b_iz^{-i}}{\sum_i^{N} a_iz^{-i}}$ and returns coefficients for $N/2$ second-order filters $H_k(z)=\frac{b_{k0}+b_{k1}z^{-1}+b_{k2}z^{-2}}{a_{k0}+a_{k1}z^{-1}+a_{k2}z^{-2}}$ and a gain $g$ such that 

$$
H(z) = g \prod_kH_k(z)
$$

So, regardless of what normalization you want from the function (none, inf or two), the above always holds. So to answer your questions:


the gain of each filter section is different (i.e. not necessarily one). (But, you dont care about that)
you do not need to adapt the gain between the filter stages. What comes out of the first stage is directly sent to the second stage. Then, after all stages were processed, you multiply the outcome of the last stage with $g$, what you receive from the tf2sos function.