The current 3(KSA, Pakistan, Turkey) should just stop accepting all additional memberships for at least 10-15 years...and only allow interested countries an observer status...
...in these 10-15 years the 3 current member states should work extremely hard to develop synergy(NATO style). Frequent training exercises, increasing(all new acquisitions) interoperability, buying each other's equipment(like drones, artillery, etc) as much as possible to keep the money circulating within and helping each other's defense industries rather than money flowing out, and have more JVs.
...additionally all 3 should allocate funding to develop SSBN(MILDEN or some other sub) and SLBMs. These would be operating under joint command...and serve as a second strike platforms(deployed around the world) to provide guaranteed nuclear deterrence IF any of the 3 member states are attacked first with nukes.
^while all of the above is going on. The observer countries(interested in joining) are told to steer their military towards interoperability/compatibility with the 3 member states over these 10-15 years while the 3 original countries are developing credible mutual defense capabilities. These countries should also be encouraged to buy defense equipment from the 3 member states when and where possible...which will add to their efforts of interoperability/compatibility and at the same time increase inflow of money towards the defense industries of the 3 member states.
Once the original 3 members have achieved a decent joint defense capability with nuclear umbrella (for the 3 original members)...then the observers can be considered on case by case basis to be added to mutual defense pact. Their military capability and level of interoperability would be taken into account as well as the risks of adding them into this pact(their ongoing geopolitical conflicts and situations) and their geographic significance(e.g. suez canal control that Egypt has) and economic conditions and the political tilt/alignment of their rulers.
...and depending on all of that...it should be determined if they are to be added only conventionally for joint defense or also offered nuclear umbrella(the two options being separate..and nuclear umbrella not just easily offered to anyone and everyone).
@Oscar would love to hear ur thoughts on the above
...objectively only...setting aside things like the incompetence of Pakistani political leadership that rears its head almost everywhere.