I'm assuming your buddies at XJT are on reserve. If that's the case, they only get 11-12 days off a month. Now, they may not get called ever day on reserve so assuming they live in base, that's another day at home. If they're not on reserve, with 18 days, they are most likely getting relief lines, which are built from open trips. Relief lines can be very good but they don't always work out. What you do is send requests to Crew Planning for what you desire for the month. Then they build a relief line per your preferences. But it's all done in seniority order so if you are low on the list and there's nothing to meet your requests, they give you what's available.

Most regional companies have similar Crew Planning practices, with various minor differences. So basically, most companies build and assign lines in a similar fashion. I'm not sure any regionals have Preferential Bidding (PBS) which is essentially a relief line for everyone. The VAST majority of pilots don't like PBS. Once the lines are awarded, companies vary all over the place.

Trip trading at XJT is fairly easy, assuming you are trading 2 trips that start on the same day. If it's a trade for a weekend trip to a weekend-off trip, it can be very tough.