Should those present reply to the words of the adhan given before the khutbah?
They should remain silent, and not answer the adhan. This is the precautionary ruling. However, if one replies in their heart (silently) and not by their tongue then there is no harm whatsoever. Only the Imam is allowed to reply to the words of the second adhan (for the Khutbah). In the Hanafi Madhab, it is not allowed for the muqtadi to do so.
And Allah ﷻ knows the best
Imam Ahmad Rida Khan رحمة الله تعالى عليه
Translation by Dr Musharraf Hussain Al-Azhari Translator of Majestic Quran, www.majesticquran.co.uk