Well Grand Tuhon Leo T. Gaje is the lineage GM of Pekiti Tirsia, and GM Jerson "Nene" Tortal is the GM of Dekiti Tirsia Siradas. The two men are related (and related to my ex-wife), and they have worked together in the past. You may find some similarities in their methods, but their approaches are somewhat different.
I have two very good friends who are both Guros under Tuhon Jerson "Nene" Tortal. They hosted Tuhon Nene for a seminar back in June 2002 - which I attended.
Just for the record, I am a student of Pekiti Tirsia under Tuhon Bill McGrath. So I can only speak of the difference between the two arts from the perspective of Pekiti Tirsia as taught by Tuhon Bill McGrath. With that being said, the two arts are really nothing alike. The basic strikes, the footwork, and the different strategies for close, middle, and long range are very different. The only striking similarity is that they share a drill but even the particulars of that are different.
They both move very differently as well - this is pretty evident on the Contradas video tape from Lionheart. For those that have seen the tape the drill that is shown for single stick/sword exists in all three arts - Pekiti as done by Tuhon Bill McGrath, Pekiti that is currently taught by Tuhon Leo Gaje, and Dekiti as taught by Tuhon Nene Tortal. Of course the emphasis, footwork, and place it has in the overall art is (I'm pretty sure...) very different.
Also, at the seminar, Tuhon Nene defined his art's name as follows: Dekiti - close range; Tirsia - options in fighting; Siradas - closing the door (to stop an attacker or to not allow the attack to penetrate...). I hope this helps.
Wes modestly omits that he is a Mataas na Guro in Pekiti Tirsia and teaches in Boston. I've had the pleasure of training with him for the past year at a year-long series of Pekiti Tirsia espada y daga seminars that have been taught by Tuhon Billy McGrath in Fishkill, New York.
I just got a flyer stating that Jerson "Nene" Tortal will be giving a two-day seminar in my little town in two weeks, and that P. Greg Alland will be a guest.
I don't know anything about Dekiti-Tirsia Siradas.
I'm planning on attending this seminar--the info. is at www.kalisilat.com if anyone else is interested (Terre Haute, IN). The advertising is a bit loud but Mr. Tortal and Mr. Alland are big names for my small and isolated town of less than 60,000.