I would never criminalise a family member who puts someone out of their genuine terminal suffering when asked to, whether doing it directly, or assisting them, or going to Switzerland. The cps have discretion to decide if it is prosecutable as manslaughter.
I would never "kill" someone in those circumstances but recognise that others would, but that happens with palliative care, Switzerland, and in extreme cases when a family members kills the person direct. Plenty of discretion within the existing law and CPS guidance to take appropriate action, or none at all.
Then what's the problem with putting the framework in place beforehand?
It stops the individual suffering, and relieves the agony of those who may spend months/years in suspense for simply helping out a person they love!
Why should someone have to end their life in a foreign land as opposed to in their own home?
And are you now saying that palliative care is a form of assisted dying/killing?