Is it permissible to prepare an iftar meal for fasting people in a mosque in Germany instead of slaughtering two sheep for the 'Aqiqah, given the difficulty of slaughter in that country?

The 'Aqiqah (definition) is a Sunnah (definition) (recommended act), not an obligation. The basis for it is the saying of the Prophet, peace and blessings be upon him: "With the boy is an 'Aqiqah, so spill blood for him and remove the harm from him," and "Every child is mortgaged by his 'Aqiqah; it is sacrificed for him on his seventh day, and his head is shaved, and he is named." Feeding fasting people is a good deed with great reward, but it does not substitute for the 'Aqiqah, which requires slaughtering an animal. If you are able to slaughter for your newborn, then do so. If you are unable, there is no blame upon you for leaving it until you are able to perform it.