Well I can't pretend to have inside knowledge of SNI organisation, but can offer a few observations.
A summary from March 1944 shows the Brigade including four Battalions, each 945 strong with;
45-mm atk guns – 2
50-mm mortars – 9
82-mm mortars – 9
Atk rifles – 24
HMGs – 12
LMGs – 37
SMGs – 210
flamethrowers – 18
Now the Red Army was not as liberal with LMG issue as most others, so you can pretty much guarantee the Bn was built around three Rifle Coys, each of three Rifle Pls, each of four Squads, with one LMG per Squad. You can't extrapolate Squad size, but there are a few examples from Red Army Rifle Brigades.
The April 1942 Bde used a Platoon with 51 all ranks;
Officer (SMG), Senior Sgt (R) and Messenger (R) at Pl HQ.
Four Squads, each Sgt (R), Junior Sgt (LMG), Asst gunner (R) and nine men (2 SMG and 7R). Across all four Rifle Squads two riflemen had sniper rifles.
There was a later Rifle Brigade org, full details for which I don't have. A summary shows the Rifle Pl as down to 45 men, with four Rifle Squads of ten each. Purely guessing from developments elsewhere, I'd move the two snipers up to Pl HQ to make it five and delete two riflemen from each Squad. Once you get into 1943 there's also the policy of switching whole Platoons from rifles to SMGs, which might impact one Pl per Coy.
Now the Naval Infantry might have had their own unique set of shtat quite different to the army versions, so make of that what you will.
Gary