You are in something of a quandary here:
They are kind, good people
As well as:
now I cannot ask them to reduce the time they spend in my room
But that is exactly what you will have to do.
I expect they will be (very) willing to allow you room for your own life. You will have to clearly communicate your boundaries while making equally clear your appreciation of them as companions.
If you do not it will erode the friendship and will block you from enjoying the good that they bring to your life.
So, how to communicate this message in a positive way? (Exponentially easing it to be picked up!)
First and foremost, friendship like this cannot be 'paid for'. But what you do need to do is to keep up your side of the shared living experience.
You just need to shape it so it suits you as well as it suits them.
You will need to have a talk.
Explain you need a little room. Ask them if that is OK. Agree upon a non-intrusive way to indicate boundaries, like a little turn-card on the door handle that they use in hotels. In addition best also mention that you wrestled about mentioning this because you value the friendship very much and are (really) afraid that this (very real) need may get in the way.
Balancing the boundaries.
Be sure not to abuse the privilege! Be available when you can, isolate when you must, and check back if it (still) works for them too.
If you still have the feeling the situation is unbalanced, throw a bash to enhance the shared living experience, like (random example) a Chicken Vindaloo-Red Dwarf binge night once a while.
In (the unlikely) case they are uncomfortable with giving you some room, it is best to have it out in the open instead of wholly on your shoulders. But be prepared to move out of the house if that is what it takes. It should save the friendship, which sounds to be of the un-moneyed valuable type, and it will save you a whole lot of stress!