I have seen elsewhere that it is a pun and can be loosely translated as either Frieren's at the funeral or Frieren caused the funeral. But I don't really know enough Japanese other than to say those are fairly liberal translations.
葬送 (sousou) literally just means funeral, フリーレン is Frieren and the の (no) in between usually indicates possession in some way.
One of the things that I think make this series better than a generic harem series is that Rentaro is a fantastic MC. He always goes above and beyond to make everybody happy. He never uses the looming threat of their death if they reject him to influence their desire to join his family. Really looking forward to this series if they keep it as wild as it has been so far. The crazier they get, the better.