I have a few questions about lore if anyone wouldn't mind replying:

-Slavery is illegal in Morrowind at the time of Oblivion right?

-If so, would there still be illegal slave trade going on?

-Finally, would Ordinators ever be involved in something illegal?

Yes.

Probably.

They've probably all committed suicide after the fall of Indoril.

What is the Fall of Indoril?

Indoril: one of the 5 houses of Morrowind. They are VERY hardcoe Tribunal. Heck, when Vivec allowed Morrowind to be annexed by Tiber Septim, most of them committed suicide. Also, most ordinators are from house Indoril. During Oblivion, there is a rumor going around that a bunch of the other houses, other than Redoran, are now taking Indoril lands. The logical explanation of this, is that Indoril as a great house has fallen, most likely due to more and more of their members committing suicide.

As for your questions

1) Yes
2) I can see the only difference is changing the name of "slave" into "forever a servant"
3) Well...there was an Ordinator that helped you in the MQ of Morrowind, which at the time would be considered illegal. Would they do something like murder someone in cold blood, they easily and probably have. All they would need to do is make an excuse that the person they killed was guilty of X crime, and had to be put down. Otherwise, I don't see them doing what the Cammon Tong, Thieves Guild, or Hlaalu would do.

So it is possible that some of the Ordinators would still be around to defend from the other great houses? Even if it is very, very few?

Ordinators are not solely Indoril, though they make up a large part of it. Some of Hlaalu and Redoran do become ordinators. And the land grabs are not from war, but from what I'm deducing, them being kicked out because they're pretty much falling apart and a bunch of estates are probably left in shambles, ruins, or abandoned, or political grabs. Heck, those still alive are probably making a switch into new houses with the way things are going.

Due to only a single drop of dialogue in Oblivion about Hlaalu and Dres 'picking apart the carcass of Indoril' do we get the assumption that Indoril is dying. My colleagues are making the logical leap that that would apply also to Ordinators, however, I'd say that those that were already Ordinators and dedicated to the Temple in that way would not commit suicide over inter-house politics.

Remember, that the Ordinators are designed first as the will of Almalexia, second to protect the Temple, and third to provide a means of third-party justice towards petty inter-House squabbles so that the small things do not escalate into House warfare.

"-If so, would there still be illegal slave trade going on?"
Slave trading? probably only among the more provincial of Dres and Telvanni holdings. Slave keeping? Probably widespread, but again more in Telvanni's and Dres' holdings than anywhere else.

"-Finally, would Ordinators ever be involved in something illegal?"
Ordinators are just people, like everyone else. While they all seem to take themselves way too seriously, not all of them would be above bending the law for their benefit. But remember that like any corrupt authority figure, they would not risk their position or power, they would use their power to ensure that you did not endanger them.

I feel inclined to agree with Mehrunes Dagon on this matter, although it is suggested that House Indoril is not doing very well (other than the part about Hlaalu and Dres picking apart the carcass of Indoril, there's also the part where it's said that "Indoril is in ruins".) this does not mean that all Ordinators would commit suicide due to the fall of Idoril, I'm sure that there are many of them who would not let house politics become a reason to end their lives.

And yes, Ordinators certainly aren't beyond doing illegal things, I doubt many of them would openly engage in the slave trade, once it has been made illegal, in the interest of maintaining public image and their position, and even in the time of Morrowind, we saw few signs of the temple keeping slaves, mostly it seemed to be Great House nobles who employed slave labor, but, like any law enforcement organization, there are still those among them who would break the same laws they enforce if they can benefit from it, and bend those laws enough to avoid trouble or cover it up.

I don't think he was saying they would commit suicide because of house politics. More likely because their religion collapsed and they were the most devout peons.

That is exactly what I am thinking.

I think that if the Dunmeri faith were in crisis, you'd hear something. Of course by the time of Oblivion, it could be old news.

Ordinators doing illegal stuff, I'm not sure...
Aren't they pretty much the law, as in they decide what's legal or not. Or does someone else decide that and they just reinforce it?

I believe the idea that many Indorils have committed suicide arose from a single little rumour in Oblivion (or something comparable), but every time I hear it, it seems to have been blown further out of proportion. The idea that the Ordinators killed themselves en masse is completely baseless.

The mass suicide was fanon that people repeated until it became fact. The suicides took place after TIber Septim's armistice, IIRC.

There's a Dunmer priest in one of the Cyrodill chapels who mentions he came to Cyrodill to join the Imperial Church "after the collapse of the Temple."