I’m not related to the family. I only try to help finding persons for people abroad.
The surname “Middelkamp” is probably of Dutch origin. But I’m not totally sure. In German the name would be written as: “Mittelkampf”
According to the Dutch institute, who are researching surnames, the name “Middelkamp” is an address name. That means that the name is of a farm, a street, a house, an area etc..
The birth record of Gerrit Middelkamp, 1878, is not a baptism record, but a civil birth record made by the town he was born. The civil registration of births, marriages and deaths started in about 1811 by the towns in the Netherlands.
I send you a copy of the original civil Dutch birth certificate of Gerrit Middelkamp, 1878.
I made a tiny translation of the main in this original. Also attached.
I did not looked for the younger brother of your grandfather, because I do not know his given name. But maybe I can find him also.
Best regards and tot ziens,
Robert A. van Duuren