Typing on an iPhone so sorry for the spelling errors,
Try PACE for a suggested System...
P for probe, " what altitude we flying at?"
A for alert, " the msa in this area is 2,500 ft and we are in cloud at 1,500"
C for challenge, "bob we are below , there is rising ground ahead.. we are in danger, you have to climb. "
E for emergency action... "I have control"
Try to involve them personally , give them an out, they may be at maximum capacity and have no space to think... Highlight their responsibility to others, hey you may be happy down here but I'm a chicken so can we climb now... Etc