You can't. On red he will always target Seeker first, and on blue he will always target Deacon first.

Thankfully doesnt matter with that comp.  As long as Heiress doesnt take the stun doesnt matter who does. 

ok, I came out that cleanse should solve all the issues BUT...

I actually do not understand why the comp always fails except with spirit.

EITHER the speed tunes! (3:1 / 2:1)

TEAM: 

1. Deacon L - 207
2. Demytha - 294
3. DPS - Geomancer - 258
4. Heiress - 269
5. Seeker - poison set - 185

NOTE:

1. according to speed calculator things should go fine but it does not
2. with spirit 3:1 tune works with low damages (only 40M per key)
3. with every other affinity tune breaks, I believe for a wrong stun
4. 
   
   1. can figure out why if the stun goes on seeker/deacon, Heiress cleanse is not working
5. NO TM/cooldown masteries 
6. NO cooldown sets (only impulse on heiress)
7. all the skill have been set properly, according to the DWJ's guide: just setting OPENER, not strictly priorities on everyone with just 2 skills 
8. 
   
   1. heiress: OPENER A2, not OPENER + 1 on A2,
   2. demytha: OPENER A3, A2 - 1, A3 -2
   3. seeker: OPENER A1, A2 -1
   4. deacon: OPENER A1, A2 - 1, A3 - 2

can someone help me figuring what I am doing wrong??!?!?!?!  

Do you have a discord account?  Much easier to help you troubleshoot there. 

mm_ambrogi

i have been told IMPULSE set on heiress can be the cause (BTW)

Impulse would definitely be an issue, likely not the only one though Id say.  Probably a speed thing. 

as for now it highly seems it was the problem.

re-geared Heiress and, as for now: either FORCE and VOID have been completed with 50 rounds...

now I will have to figure out how to increase damages..

as seeker and heiress are around 16M, but GEO only 19...

Glad you got it sorted.