Think through what might be in the mix here (it's a guess, by the way, but based on memories of being a parent to that age, and now hosting a nephew coming up to the same age).
Both parents don't seem to be getting much sleep - this could now have been the case, on and off, for up to 3 years. Nobody is at their best in this situation so they might not be all that happy in conversations and don't mean to be short with you.
Hosting anyone while also being parents to small children is an extra stress for most people anyway. It's lovely, but it does throw many curveballs.
If a 3 year old takes it into their head to climb out of a cot after escaping from a sleeping bag, it's possibly dangerous, but it's extremely difficult to stop this. Extremely. When DNeph stayed overnight recently (with parents), they managed to do this from a travel cot (canvas sides, not bars) while also holding a soft toy, and go downstairs. Almost no vigilance is going to keep a lid on this. So don't open the channel to 'get out = go downstairs to find grown ups is an option' instead of back to bed. At the climbing phase, even as a parent, there will be points when you won't believe what will get into their heads in terms of a 'safe, fun climb' in what looks to be a normal environment. The best case scenario is that something ends up in chaos (like climbing from a bath edge to a sink - real example).
If DGC is a poor sleeper then naps will still be important for everyone's sanity; the parents will have found this out already.
They don't mean to be mean, but they're the ones who have to function whether you are there or not, by way of their parenting techniques vs toddler's stage.