Fr. Paul Kramer is sedevacantist (at least to my knowledge) and says that saying the pope is the pope (i.e. naming him in the Canon) would be "proximate to heresy". Besides that opinion, he's pretty orthodox in his teaching otherwise.
I didn't list him on dubia because (a) he was pretty hard sede and (b) I thought he was retired and couldn't find any Mass locations, I think he's in Ireland. I put him as "independent / retired", not sure about his ordination, but he did some interviews on YT.
(a) No he is not a "sede" as is typically understood. He considers John XXIII to Benedict XVI as Pope, but Popes that suspected of heresy. However, Francis, he considers was never Pope and Leo, he considers a Doubtful Pope.
(b). Correct, he is retired and living in Ireland.
(c) He was ordained in the new rite by a bishop consecrated in the old rite. Similar situation to Fr. Hesse, as both graduated from the Angelicuм. Bishop Williamson, Tissier and Fellay all said conditional ordination was not necessary in their case.