Don interpreted you as saying the 1984 house was moved in 2000 - in which case his comments are right on the mark as always.
I interpreted it as being a 1984 house, and you move into it in 2000, but that it is in original location. If you do not have a crawl space or basement, then you are on a slab foundation on grade.
Since the cracks seem to be be growing and are diagonal at door frames, the normal cause for this is differential settlement, usually caused by slab settlement or by creep or sagging in supporting beams or posts.
The kitchen (darker brown paint) one looks fairly typical of settlement at the right of the doorway, relative to the doorway. The doorway in the hall is odder - because the crack goes right up from the doorframe to the ceiling and across the ceiling, it looks to me like there is no header over the doorway - which would be against code, and if the hall wall(s) are load-bearing could be causing the attic trusses/joists to sag down on the doorframe, causing the crack up the wall and into the ceiling drywall.
IF this were a typical California post and beam crawlspace house, I would be looking for settlement, dryrot, ground squirrel undermining or termites damaging the supporting posts or beams under the floor. Since it sounds like a slab floor (if you have no basement or crawlspace), then could be slab settlement, or improperly framed doorways, or some other source you could only determine by an on-site visit. (BTW a crawlspace might have an outside entrance door, typically if furnace is down there - or might only have an access hatch in a closet floor or through the exterior foundation wall which you might not know about. If you have a crawlspace, you will have concrete or block foundation walls rising out of the ground to typically 2-3 feet above ground to where the house framing (and siding or stucco or whatever) begins, and would have screened openings through the foundation wall for ventilation. If a slab foundation, your house is built on a concrete slab that site at ground level, so you would see only the edge of a 4-16 inch thick concrete slab edge, with the framing directly on top of that.
One other possibility, especially if all your substantial cracks line up in a more or less straight line across the house (but not necessarily parallel to the house face) is if your house is built partially on fill and partially not, it could be due to slippage or settlement of the fill, causing a slight tilting of one end or side of your house. Obviously, if your house is a hillside or cliffside house this is a more likely cause than otherwise.
Since you say the cracks seem to be growing in a 30 year old house, even though at this point I do not believe they are immediately indicative of anything serious, I agree you should have a structural engineer look at it, as Don suggested.
The first thing I would be looking in an inspection would be the foundation type and the crawlspace supports if any. If slab on grade construction, I would (and you could easily do this too) I would peel back the carpet right below the cracks, pulling it off the carpet tack strips (watch out for many little nails sticking up, which the carpet is pressed down onto to hold it in place) and looking for cracking in the flooring or slab under the carpet. These inspections (whichever is applicable) combined with a walk-around looking for foundation cracking visible from the outside would almost always quickly answer the issue of whether you are looking at a foundation issue. IF not a foundation issue, then likely an interior structural issue which I would address with a stud finder, looking at the spacing of studs and existence or non-existence of proper king and jack studs alongside the doors, and proper header and cripple studs over the door (image of terms here) -