Using RNRB on first death

Continuing the discussion from Kessler precedents re RNRB gift:

I have been reading this thread, which goes a some way to providing me with a way forward, but hoping for some clarity from forum members as I am tying myself up a little.

Options seem to me to be:

Absolute gift of share of property equal to RNRB to lineal descendants.

IIP of share of property equal to RNRB to lineal descendants.

There is then the IIP with revocation to DT. Not sure there would be the CLT charge issue mentioned as would only be £175K. However, I am not so keen on this option as could be an issue and would need to consider previous future planning by the lineal IIP benefs.

The Flexi Qual IIP - I presume as well as direct lineal descendants, who take as IIP, the spouse is named as a potential benef so property element could be appointed to them if required? But this does allow claiming RNRB on the first death.

Then there is the GNRB on DT coupled with a 23 month DT for the RNRB to allow appointment out in 2 years. With this, seems to me that while giving flexibility (which is always useful), the RNRB could only be claimed if appointed out to lineal descendants as not qualifying for RNRB under the Will as to a DT; meaning decision made as part of IHT 400 prep etc.

I may well be wrong with my understanding/summary, so happy to be corrected where that may apply. And any other suggestion/explanations greatly received

Thanks in advance