'Holy place' is without an article and characteristic. The Greek does not designate some particular place. I have inserted 'what is a' to generalize it.
Or 'consider [it]:' see Mark 13.14, and Note c.
'If possible' gives the purpose of the deceivers; 'if it were possible' would be the judgment of the writer. It seems to me simpler to take it as in text. It still implies 'it is not possible.'
A strengthened negative, 'in no wise,' 'not at all,' as in ver. 35.