Patricia is the granddaughter of Pierre Guerlain. Jean-Paul is the grandson of Jacques Guerlain. Pierre and Jacques were brothers (sons of Gabriel, who was the brother of Aimé). So yes, Patricia and Jean-Paul are related, although I've no idea what you call this relationship English, or even in Hungarian
It looks like Jean-Paul, who retired in 2002, is indeed the last of the line. He does have a son, but he's a lawyer. Thierry Wasser was named in-house perfumer of Guerlain in 2008 and still holds that position. According to Wikipedia, "Jean-Paul Guerlain is staying on in an advisory role, as a counselor to the presidency, for both fragrance design and ingredients."