Question: From death to brittleness?

Two bodies, on a bed, in an embrace. Windows and doors closed, so little to no air and light, but not completely air/light tight.
No scavenger animals/rodents, but bugs would obviously be present.
Humid (tropical rain-forest) environment.

The aim is to have my characters stumble across this old castle, and find the bones of two people on the bed. I don't care if the bones are touched they would fall to dust, or if they are moved slightly/disturbed by bugs, or even if some of the bones are dust already, as long as it can be made out that its two skeletons embraced together. (and if not clearly embraced, its at least clear that its two skeletons)

(i know "dust" isn't the appropriate term here, but you get what I mean?)

How many years could this take?
Thankyou

EDIT: Just wanted to re-iterate, I don't so much care about the decomposing bodily fluids and flesh. I know that will decompose and be eaten by bugs and will stain the sheets upon decomposition.

I know that mummification is out, as of the humidity.

I'm wanting to know what happens to the BONES well after the process of rotting flesh is done. I know the joints wont stay together, and I know that the bugs will move the bones around a bit if they are eating the flesh. But say that, after a month or so of the people being dead, their bones would still be on the bed, and it would be obvious that two people were on the bed together, even if not embracing?
how long would it take before their bones became so fragile and brittle that they would turn to "dust." or upon discovery of the bones, and disturbing the bones, would they disintegrate to dust upon a rush or air or a touch of hand?

Answer: 
It really depends on four things

1. how well sealed the room is, keeping rodents out is essential, they will eat bone just for the calcium.
2. the humidity, fungi can eat bone so you want it dry, light is likewise the enemy.
3. the temprature, if it is exposed to freezing and thawing the bones will powderize quite quickly. so it needs to be consistently above freezing or consistently below, dryness will also help.
4. how much anatomy the people finding them know, the more anatomy they know the worse off the bones can be.

As long as only bacteria or small insects can get to it bones, and it is dry they may survive intact (identifiable) for 300 years as long as they do not go through to many freeze/thaw cycles. basically the better the conditions are for natural mummification the better they are for your bones. 

Your biggest problem is the tropical rain forest, the bones are gone unless they get buried, heck even your *buildings* are not going to survive that well in that environment. Bones a month sure, a hundred years highly unlikely. The more cave like the place they are they better they will survive in that climate.

There is one way to preserve the bones, but they will not be easy to find afterwards. Guano can seal and preserve material in a similar fashion to amber, but you need to keep it away from the sun and it needs to build up quickly. so you need a lot of bats, possibly coming in through a hole in the roof to keep the rodent population non-existent and keep out the most destructive insects (ants and termites), for this same reason your building needs to be big. The downside is that your bones will then be buried, so unless your people are looking for them they will not find them. 

bones turning to dust requires a very dry environment, you need to keep biological activity to a minimum. I have handled fossilized mammoth bones in Wyoming and you could crush them with your hands and they were constantly flaking off bone. They were buried in almost 3 feet of natron soil in an extremely dry environment.
The rule of thumb is “100 degree-days to get bones”. I don't know what *degree* is measured from, but that should be a start for Google…

And that turns up [this link](https://weather.com/science/news/flesh-bone-what-role-weather-plays-body-decomposition-20131031) which is a start. [This one, *The Rate of Decay in a Corpse*](http://www.exploreforensics.co.uk/the-rate-of-decay-in-a-corpse.html) is more informative and provides the vocabulary you will need for further searching.

Just skimming, the lack of rain or direct exposure and not being directly connected to the soil will reduce the decay rate. Depending on conditions you may bet a mummy and not a skelleton.

So allow for **rats** or other wildlife to get in from a wooded area, as well as flys and beetles. That's the opposite of what you specified, so you can expect dessicated remains with nothing happening after flys. You might postulate specific carnivorous beetles, but really you wrote yourself into a corner. Where would the flesh hqve gone off to?