This is, indeed, the family Temple for Masamune and all his lineage since then. This is my family, we have a direct line through the Yamamura family of swordmakers back to Masamune.
The photo shows Takeshi Yamamura Swordsmith 24th generation since Masamune. He is the current swordmaker in Kamakura. He showed us all the tombs of the entire family - all marked with the family mon of a round circle with two lines. This depicts the full moon with two strands of cloud.
100% correct information about Masamune at Hongaku-ji Temple, Kamakura.