I have a Himalayan and a Maine Coon, and they both tend to get matted on the side they like to sleep on and from roughhousing.
Neither likes being brushed. One runs and hides under the sofa, and if he can’t do that he bites; the other commits murder. So it goes.
Each gets professionally groomed once a year. The groomer has a useful humane restraint technique that you may be able to use at home if you have a savvy and brave helper. She uses a slip collar and leash and has an assistant hold that in one hand to prevent the cat from leaving the premises. Then, she rolls up a washcloth behind the cat’s ears so that the cat can’t easily see what’s going on behind him. This both discourages “I am anxious about what I see you doing, and I think I will not like it, so I will kill you” and also prevents them from aiming well. Finally, when they get rowdy, the assistant does scruff them.
This works very well and with this technique both boys can get a full-body brush-out and hygiene clip in 20 minutes.
At home, maintenance is accomplished with “brushing over breakfast.” While the cats are face-deep in their kibble, I spend about 15-20 seconds brushing each one until they get restless. This sounds like a little, but it does add up to keep the shedding and matting at bay. And any time they need to go in to the vet I ask for a hygiene trim while they’re there- that makes a big difference in maintaining the pantaloons. If there are multiple cats, brush brush treat may be a little more difficult because my experience is that the other cat will bully in for the treat and then they have to have a philosophical debate, but a) your friend’s cats may be less rough-and-tumble than my boys, and b) this also goes much better if your cats cannot open doors.