La loi vous oblige à désigner un Syndic, qu'il soit professionnel on non.

Je dirais plutôt, vous devez en assumer l'entière responsabilité.
En tant que Syndic, vous avez également l'obligation légale, que vous soyez Syndic bénévole ou rémunéré, de prendre une RC Syndic, afin de couvrir vos responsabilités.

Imaginez qu'il y ait ce soir un incendie ou un dégâts des eaux et que l'on vous reproche en tant que Syndic, de ne pas avoir assuré votre copropriété?

Ceci constitue une faute grave!!

Vous avez signé ce prêt de manière solidaire 50%-50%?
Votre "compagnon" est votre mari ou cohabitant légal?

Yes, it is!

But I am extremely surprised that "students" have taken such an apartment in WSP.

For the apartment I am renting out in WSP, I have never had Belgian tenants. Belgian candidates who can spend more than 800€/month, become owners (of course not in WSP).

Also no "students" or unemployed people ...

My tenants have always been wealthy expats working for European HQ of American (or other) companies (like Bank of New York Mellon, Cisco, Toyota etc...)

Never Belgian students! They rent "kots". Unemployed people in WSP can apply to get a social home.

Is the rent paid by their parents? How old are they?

As soon there are different owners, you are in a forced "copropriété".
By law, each "copropriété" needs to have an "acte de base", a ROI (Règlement d'ordre intérieur), a Syndic and a registration number at the BCE.
When you have bought, your notaire had the obligation to provide to you the official "acte de base" ; the "reglement d'ordre intérieur", the PV (minutes) of the 3 last Annual General Assemblies.

Did you get those extremely important documents?

Of course, the whole building belongs to a single owner; so you are not in a "copropriété" having an official "acte de base".
By the way, did you apply to get an official permit to divide your "Maison de Maître" into separate apartments?

Well if this is true, you have been had!!

I do hope for your that they don't maintain their drinks cool by putting the bottles in the lavabo and leaving the taps open all days long...

May we know the amount of the rent and the fixed monthly amount to cover all the service charges?

For how many sqm?

Since how long are they in your flat?

After 1 year, they will probably get a huge adjustment bill since in Belgium, electrical heating is much more expensive than any other energy.

I do hope they have private electricity meters at least...

Faux, cela peut être pris en charge par l'assurance "incendie" de la copropriété (et non du Syndic) s'il est avéré que l'origine du sinistre réside au niveau de la structure.

Maintenant si la fuite a été provoquée par un manque d'entretien du propriétaire/locataire précédent (débordement de la baignoire, d'un évier, non remplacement d'un joint défectueux etc...), l'assurance "incendie-dégâts" des eaux de votre copropriété refusera d'intervenir...

D'où l'envoi d'un expert...mais s'agit d'un expert mandaté par votre assurance "copropriété"?

Qui prend en charge ces frais de recherches?

A quel titre votre Syndic s'oppose-t'il à ces recherches?

Le syndic n'est que le bras qui exécute les décisions prises en AG par les copropriétaires.

Let's be serious.

Your tenants have asked to the Judge a "résolution du bail", which means to be able to break the lease without having to pay any indemnity.

You desperately want them to be evicted.

So why not sit together and sign a document confirming both parties agree to break the lease without having to pay any indemnity?

Giving your health problems, you can avoid to have to support a legal procedure, that can takes months before to get any decision from the Judge. Moreover, you don't know the Belgian laws on renting (Main Residence) and you are not fluent nor in French nor in Dutch.

+ Given the fact that your case is extremely weak and that Belgian laws protect extremely well tenants who have a 9 years contract for main residence purpose, I would avoid by any means to have to go to Court!!