I've had severe demand avoidance my whole life. If people interrupt me or keep trying to get my attention without considerable breaks, I get quite overwhelmed. I mean that I can easily go into a complete meltdown if someone continues to interrupt me after I've asked them to please stop, even if their interruption is seemingly helpful and selfless.
I seriously broke up with a girl that loved the hell out of me because she just couldn't stop interrupting me when I was engaged in something. I completely blocked another friend I had for ~17 years after going on an international trip with him because after asking him repeatedly to please stop blurting out every single idea he has, to save them until I seem like I want to hear it. Nope, he just couldn't do that. It is just completely unbearable for me, and after leaving the trip on my own earlier than planned, I blocked all opportunities for him to contact me. I would be happy to never hear from or of him ever again. That's how much I cannot tolerate demands.
Aside from that, the best part of my day is when I go to bed to lie down for the night. It is my safe place where I know no one will interrupt me because everyone is asleep. This happens even if I live alone.
Unfortunately, the way this plays out is that I end up isolating myself and have pretty bad sleep issues since I basically stay in bed awake for hours at night. It's like my body wakes up once I hit the bed, which is terrible for sleep hygiene. Last night, I went to best at midnight and didn't fall asleep until 5am, so I'm exhausted-tired today.
I'm working with a therapist to develop a social circle that is healthier for me, so that's on the horizon...hopefully. When I review my life, my favorite relationships are ones where I just co-exist with someone in the same space without much direct verbal interaction. I enjoy touch and sharing, but not if they talk a lot. And if they do talk a lot, I prefer if they keep the talking consolidated rather than spreading it out throughout the day. I can tolerate 2 hour conversations wayyy better than 6 hours of talking for 5 mins repeatedly.
Any other suggestions on how to manage this?
I don't know you or anything about you but what you said, but holy shit. If I was in your care, I would end up more traumatized than before.
Boundaries are a thing. If people refuse to accept boundaries, as some therapist and especially nurses like very much to do, they are toxic. If someone tells you they don't want to be interrupted sometimes, respect that. Don't go all "I know what's best for you", unless yop're talking to a literal child - and even then think about whether you're just telling the child what to do because you don't think it should be doing what it wants or because it's really better for the kid.
Some people need alone time. It's called introversion. An international trip with constant blabbering sounds like a nightmare. I'm imagining they had booked a double room with no option for OP to withdraw. I would melt down in two days.
Not everyone is maladapted and blaming others. Some people have good reason for what you deem unreasonable demands. I don't know if your client are full-blown adults or have a handicap where their judgement is impaired somewhat, but I want to encourage you to stop and think whether what you're teaching them actually helps them and fits their individual needs or whether you you think you figured out a blanket approach that you try to get everyone to follow, no matter their mental needs.
Edit: I, too, have a relationship, a great circle of friends and a well-paying full-time job, if you want to claim authorities in something here. And I do set healthy boundaries like OP does. There is no one-size-fits-all.