Answering 'Amen' while reciting birkat hamazon

Hi,

One who leads a mezuman recites (at least) the closing line of each blessing of the birkat hamazon blessing after meals aloud, for people to respond 'Amen'.

One who is in the middle of one of the blessings should not answer 'Amen'. However, one may respond 'Amen' at a break-point between the blessings.

(Rivivot Ephraim 1:148)

Have a great day,
Mordechai

Amen after Shehechiyanu recited at Kiddush

Hi,

One who recited Shehechiyanu when lighting Yom Tov candles still responds Amen after the Shehechiyanu of the person who recites kiddush. Saying 'Amen' is not considered an inappropriate interruption between kiddush and drinking, because the berachah of Shehechiyanu is necessary for the person reciting kiddush.

(Rav Moshe Feinstein, Igrot Moshe Orach Chaim 4:101:1)

Gmar tov,
Mordechai