I think that this time, the characters of Fate/stay night and Fate/hollow ataraxia will appear in this new game Melty Blood series, as well as in Kara in Kyoukai and some of Fate/zero will also. Here is a timeline that I made based on the times in which events occurred in these series:
Timeline corrected:
Between January 31 to February 14, 1990 - Fate/zero
From August 1995 until March 1996 - Kara in Kyoukai 2 - Murder Speculation Part 1
From March 1996 until June 1998 - Kara in Kyoukai 4 - The Hollow Shrine
July 1998 - Kara in Kyoukai 3 - Remaining Sense of Pain
September 1998 - Kara in Kyoukai 1 - Overlooking View
November 1998 - Kara in Kyoukai 5 - Paradox Spiral
January 1999 - Kara in Kyoukai 6 - Oblivion Recorder
February 1999 - Kara in Kyoukai 7 - Murder Speculation Part 2
March 1999 - Kara in Kyoukai Epilogue - Final Chapter
Between 21 October 1999 to 2 November 1999 - Tsukihime
Between January 31 to February 15, 2000 - Fate/stay night
July 2000 - Kagetsu Tohya
August 2000 - Melty Blood
Setember 2000 - Melty Blood Re-ACT
Between 08 to October 11, 2000 - Fate/hollow ataraxia
From October 2000 until July 2001 - Melty Blood Act Cadenza (Neco-Arc, White Len and Neco-Arc Chaos Special Route Scenarios only)
August 2001 - Melty Blood Actress Again and Melty Blood Actress Again Current Code
- Len never gets mentioned in the original Melty Blood.
- The events that occur in the original Melty Blood take place in August 2000 (Ten months after Tsukihime), while the events of Tsukihime passed in October 1999. Already in Melty Blood Actress Again, these events take place in August 2001 (one year after of Melty Blood original).
- The events that occur in Kagetsu Tohya take place exactly nine months after the events of Tsukihime.
- I think the events in Melty Blood Re-ACT, came a month after the events of Melty Blood original (which gave Aozaki Aoko time to use the remains of blood of Zepia Eltnam Oberon, which contains the Reality Marble Tatari, in order to together with the hidden personality that she took of Len, in order to create White Len).
- Only events in the story-modes of Neco-Arc, White Len and Neco-Arc Chaos Special Route (where he faces Neco Chaos Black G666) are considered canon in Melty Blood Act Cadenza. As for the story-modes of the other characters are not really canon.
- Characters with story-modes which are within the main event of Melty Blood Actress Again Melty Blood Actress Again and Code Current (The repeformance of Hologram Summer of Night of Wallachia/TATARI in Misaki Town, performed by Dust of Osiris):
Tohno Shiki, Sion Eltnam Atlasia, Arcueid Brunestud, Ciel, Tohno Akiha, Hisui & Kohaku, Kohaku, Miyako Arima, Night of Wallachia, N, Nanaya Shiki, Sion TATARI, Red Arcueid, Akiha Vermilion, Mech-Hisui, Yumizuka Satsuki, Len, Neco-Arc (Playstation 2 route), Aozaki Aoko, White Len, Kishima Kouma, Riesbyfe Stridberg (Original Arcade Route), Michael Roa Valdamjong, Ryougi Shiki, Powerd Ciel and Archetype: Earth
- Characters-Story Modes with that happen after the main event of Melty Blood Actress Again Melty Blood Actress Again and Current Code (Following the destruction of Dust of Osiris):
Hisui, Neco-Arc (Original Arcade Route), Seifuku Akiha, Tohno Shiki Boss Rush Story Mode, Neco & Mech, Koha & Mech and Riesbyfe Stridberg (Current Code Special Route).
PS: The events of Fate/stay Night takes place after of events occurring in Tsukihime (which explains why the Bazett Fraga McRemitz and Caren Ortensia will make an appearance in future Tsukihime 2).