9 yr lease-Tenants not accepting lease termination notice

Folks,

Tenants not accepting legal notice
I am trying to break a 9 year lease on the first year with a letter as cited here

I have sent a "envoye recommende avec accuse de reception" to BOTH tenants dated last Thursday 12/4/2012.

Postoffice attempted delivery on 13/4/2012 but they have not collected it in the last four days..

B post tracking for both letters is the same since last Friday the 13th, although I know both are in TOWN, in the apartment every day

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(1) Since the postoffice attempted delivery on 13th April 11:51 hrs, can we confirm that the 6 months notice starts on May 1st?
(2) What do I do if they do not accept the lease termination?
(3) Is there any other means to notify the tenants of lease termination?
(4) Should I need to attempt another means of delivering this lease termination ?
(5) What should I do with the bounced/returned latter in case if they do not accept it?
## I can deliver in person before and ask for signature from a copy of the letter delivered confirming they have received it, but NOT sure if they would sign it
## I can just put a copy in their postbox but there is no proof to confirm if they have received it
## I can send a scanned copy of notice as PDF via email with Bpost tracking info , nudging to accept it.
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Tenant indemnity in case if he wants to break lease in this 6 months notice
The template I used for signing the 9 year contract was  taken from PIM website and the form is “contrat de bail de résidence principale pour un immeuble sis dans la Région de Bruxelles-Capitale” <https://www.pim.be/telechargement/bail_principal_v2009_bruxelles.pdf> :

The contract states that"

Now that I have given them 6 months notice for my family's own occupation, I need to know my rights what if the tenants want to leave within this 6 months notice period?

They are in the first year of 9 year lease. Second year of lease starts on September 2012.
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(6) Are they supposed to pay any indemnity in case if they want to leave within these six months notice period from May to Oct 2012?
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A clause in my termination notice
A clause in my termination notice says the following

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(7) Could somebody please clarify what it means?
(8) Does this clause anyway influence the indemnity tenants have to pay in case if they wish to break lease during this 6 months notice period?
(9) With the above clause, can they just give one month notice anytime and walk out without paying any indemnity?
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tenants conciliation request with Judge de Paix
Tenant filed the following conciliation request, date of meeting May 3rd. I have an option to postpone it for another day as I believe need to ensure that they acknowledge the lease termination first.

Water Heater problem reported below has been resolved within 24 hours of tenants gave an appointment to bring a technician.Although no technician confirmed the issue is due to old age, no technician confirmed any "gas smell", I intend to replace the water heaters at the earliest convenience.

I have a feeling I have nothing to gain from the conciliation.
I could rather have them for six months to get myself ready for the move.
Although, I am worried if they will move forward with a "requette" with Justice de Paix if I don't go for conciliation or send me a lawyer notice as they have many lawyer friends.

They don't have any strong proof either. 

(a)# I do not have proof of "entretien complete" from within 3 months of tenants occupying in Sep 2011.
(b)# I have a proof from water Heater company who fixed heating issue in October 2011
(c)# I have fixed water heater problem aagin , at my cost, albeit it is a technical issue, normally the responsibility of tenant, but I undertook to do that due to (a)#

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(10) Do I need to go for conciliation with Judge de paix(concilier) dated May 3rd (whether they accept lease terination notice or not)?
(11) Is the above query strong enough for them to quit without indemnity, within this 6 months period of notice I have given them?
(12) How fast is the requteet procedure in WSP?
(13) What if my 6 notice period ends before that?
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