Some farmers do let the collies in the house, most don't.
My two share a 2-bedroom apartment with spacious communal area (and are often together in one of the 'bedrooms' unless the owd fella is locked in his own so he doesn't steal Dottie's tea
) but are only out when needed or when I am doing something on the farm that they can join in, yes.
So they accompany me on my morning rounds, which may be 10 minutes or an hour, depending on the time of year and what's going on, then are penned up unless needed until I do my evening rounds, which are always at least an hour, often two.
Lambing is a busy time of year, so they are out and about much more, and shearing is Dottie's favourite time of year as she is top gatherer. (Skip helps but it's usually too hot for him to be doing too much running.)
Our farm is on roads with fast traffic, so I don't risk them loose unless they are with me and I can keep an eye on them.
BH's collie is on her own if we don't have a hound pup to walk, otherwise the hound pup stays with her in her 3-room apartment. BH gives them plenty of exercise, and does let them wander about the farmstead in the evening when the roads are quieter.
When I got Skip and Ted, Ted was delighted to be being upgraded to his own large apartment from the beer barrel that had been his bedroom (chained to it) in his previous home. No way was he going to be house-trainable, so I didn't try. I gave Skip the option, but although he loves to come in for 10 minutes fuss now and again, he can't cope with the heat indoors and prefers to be outside where he can fulfil his No2 duty as Main Guard Dog. (Self-appointed, he's actually nowhere near as good at it as Mist.
)
Dot is the same; she had a lot of indoors time as a pup, getting socialised and playing, and also loves to come in for a visit sometimes, but as a working adult she finds it too hot and stuffy after 5 minutes or so.
Their ideal would be kennels they can use at will and being allowed to roam the farmstead. The roads make that a non-option, not to mention that too much free time and a collie's brain coupled with no boundaries would probably lead to Trouble with a Capital T. (Which is why Skip was kept in an enclosed rear garden during the day, if I was in, at the moorland farm, and penned otherwise. He could escape the garden if necessary, but had learned that unjustifiable roaming resulted in incarceration!)
Collies do need their own space, so even if they are indoor dogs they must have at the least a cage that is their very own, where they can retire from interaction and sleep and think. Working collies need thinking time.
I have no strong views one way or the other about collies being indoors or not in a draughty farmhouse; in this part of the world, if they lived in a centrally-heated, insulated house, they'd become too soft to cope with the working conditions.
The only time I find it a problem is when one of them has to stay overnight at the vet's. They are very uncomfortable, panting and unable to settle - it's just way too hot for them. I think the vet ought to have some collie kennels in the unheated stabling area!