My opinion:
As a matter of construction, 15.10.4 determines notice period of redundancy. 15.10.5 determines minimum entitlements for redundancy. The two items are not the same. If 26 weeks pay was the minimum entitlement, it would be stated in 15.10.5. Moreover, 15.10.4(b) states that by agreement with an individual pilot, a notice of redundancy may be paid out... The word 'may' means that the payment in lieu of notice is discretionary (that is, it is not an entitlement) - so long as the parties agree.
So, a pilot who's minimum redundancy entitlement under 15.10.5 is 4 weeks would have to be given 22 weeks notice (or by agreement be paid 22 weeks notice in lieu). In 'normal' circumstances when the stand down provisions were not in force, that would amount to 26 weeks of pay. If the pilot is stood down, that notice period should attract whatever job keeper minimum payment is in force at the time.