One of these two moments has got to be the saddest one of the FMA series.
The first option is when Shou Tucker turned his cute and lively little girl into a sad and suffering chimera by transmuting her with her dog... it was Scar who found her and decided to destroy her in order to cease her suffering... and the Elric brothers were all mad and sad when they found out what happened.
The second option is when Maes Hughes, always so lively and funny, was killed by the homunculus... his family, who was very happy and cheering, suddenly felt into sadness, principally his little girl whom he was so proud of.
Any third option you have in mind, please post accordingly.
The first option is when Shou Tucker turned his cute and lively little girl into a sad and suffering chimera by transmuting her with her dog... it was Scar who found her and decided to destroy her in order to cease her suffering... and the Elric brothers were all mad and sad when they found out what happened.
The second option is when Maes Hughes, always so lively and funny, was killed by the homunculus... his family, who was very happy and cheering, suddenly felt into sadness, principally his little girl whom he was so proud of.
Any third option you have in mind, please post accordingly.