Loaders

Squad team weapon loaders must be nominated to their single respective weapon before the game and stay within 1in of their assigned weapons.

Do note that the composition of the Parachute Diversion Section was changed in the latest FAQ to include one more man (although it doesn’t resolve your question):

Page 138, Parachute Diversion Section. Composition should be: NCO and 7 men.

The weapons configuration stated in the D-Day Overlord book for the Parachute Diversion Section is:

NCO and three men with rifles, two PIATs, two LMGs

So unless the NCO is allowed to become a loader, otherwise one of the remaining 3 men must be a loader for 2 weapons. For example in the latest FAQ, the NCO was allowed as a loader for the Compagnia Sahariana Squads in the Western Desert book. However that will contradict the Squad based team weapon rule below:

Choose which model becomes the loader – you can pick any model in the squad except the NCO, …

Hence I would say the 3 men with rifles can be loaders for more than one weapon so as not to contradict the Squad based team weapon rule. This would mean (as you have pointed out) that at least 1 of the 2 PIATs or LMGs would be unable to fire in any turn without a penalty.

Finally, Bolt Action 2nd Ed page 73:

When the team weapon is fired, the loader cannot fire his own personal weapon – he is too busy crewing the team weapon.

This means the loader can fire his own weapon when the team weapon is not fired.

Your question raised a related question – can the LMG gunners be loaders for the PIATs and vice versa? I think currently the rules do not prohibit this (it says “you can pick any model“). What this means is that in any turn, the NCO, 3 men with rifles and either the 2 LMGs, 2 PIATs, or 1 LMG + 1 PIAT can fire together at the same time.

Another combination is for 2 riflemen to be loaders for the PIATs and the PIAT gunners as loaders for the LMGs. So in any turn the LMGs can fire with the NCO and 3 riflemen with no penalties, or the 2 PIATs can fire together with NCO, 1 rifleman and 2 LMGs (with penalty for LMGs only). The reverse also works i.e. assigning the 2 riflemen as loaders for the LMGs and the LMG gunners as loaders for the PIATs.