Imaginary habitable gas giant planet

Larger in diameter than the earth, but smaller than Saturn.

Denser than Saturn and Uranus, but less dense than Mars.

Warmer than Jupiter, but still cooler than Earth.

Less gravity than Jupiter

Orbiting a binary of a F-type (white) main sequence star and an K-type (orange) dwarf star. Orbit is slightly oval elliptically.

a few rings of mostly rock and some ice around the planet,
three medium/large moons of rock and ice, one with an atmosphere, orbiting the planet, along with some small asteroid-sized moons.

The planet rotates every 21 hours. The water bulges at the equator.

Planet is tilted 18 degrees at its axis.

More variable temperature than Jupiter, Saturn, Uranus, and Neptune.

Has an atmosphere of 29 percent oxygen and 68 percent nitrogen, with secondary gases being water vapor, helium, and argon. There is 0.38 percent carbon dioxide, and traces of ethane, chlorine, ammonia, and methane, and less of gases like fluorine, hydrogen sulfide, and phosphine. lower atmosphere more toxic than middle and upper.

Below the atmosphere is a layer of extremely hot, extremely high pressure ionized supercritical saline water that forms most of the planet's mass. At the center is a small core of rock, iron, nickel, and hydrogen compounds.
The planet has a significant magnetic field generated by electric currents in the core as well as the deep water. North magnetic pole is 11 degrees south of the geographic North Pole.

Life on the planet includes tiny photosynthesizing organisms, as well as large flying creatures. Life has to stay airborne, so the creatures fly day and night for their whole lives, even in their sleep, with the brain stem and spinal cord keeping them in flight.

People have to live in giant airships, either rigid (full framework) or semi-rigid (partial framework In front, tail, and lower middle). The airships can have gas of helium-3 and/or helium-4. Framework[2] of aluminum-magnesium-based alloy with a fairly small amount of lithium and zinc, and trace amounts of silver and manganese. Otherwise, framework is polymer reinforced with stishovite. The gas bag is polyethylene terephthalate in an envelope of weatherproof aluminum-cotton mixture. The gas bag is divided into gas cells. Semi-rigid airships use ballonets filled with hot air. Ballonets made of cellulose acetate. There is a rudder and elevator in the back. Ballast uses tanks of water condensed or dropped. The water can be drained for buoyancy.
Engines on the airships can be turbo-compound, mixed/dual-cycle compression/spark-ignition four-stroke[4] Miller-cycle V8 engines driving contra-rotating propellers. Use fuel high-cetane, low-sulfur B20 biodiesel(with small amounts of nitromethane and butyl rubber) stratified charge, and E15 gasohol[3] with 5% isopropanol and 10% ethanol homogeneous port injection[4]. Gasoline with small amount of MMT(8.3 to 180 mg/L) mixed in. Isooctane to heptane ratio 89:11. Dry-sump lubrication. Turbocharger with three coaxial turbines, coupled to crankshaft by hydraulic clutch. Three axial compressors feeding into centrifugal compressor. Catalytic converter[4] and Muffler used. Radiator with blower used. Intercooler used.
Engine power generates electricity.
The airships have cabins, stores, restaurants, and bars on board. The cabins have balconies looking outside. The airships have a trapeze system to launch small airplanes using catapults and land planes with tail hooks using catcher cables. Airships carry one three-seater plane, two two-seaters, and two single-seaters. Planes use turbo-ramjets.
More modern form of airships is rigid structure, also with bags at upper side, so helium is heated by flares and blown by fans. Rigid structure epoxy cured with phenols, amines, and thiols altogether and reinforced with fibers of medium-carbon, medium-alloy, high nickel-chromium nitriding steel with austenite+ferrite+martensite microstructure. Steel with 0.7% silicon, 0.95% aluminum, 0.4% manganese, 0.08% sulfur, 1% molyhdenum, 0.15% vanadium, and some tungsten.
Airships use instant cameras, and also use video recording. There are also infrared video and ultraviolet pictures. Computers are electromechanical, also with integrated circuits(transistors along with inductors, resistors, capacitors, and transformers) together with Babbage engine. Use of CD's and cassettes as well as phonographs for audio recording and playing, and multi-layer DVD as well as VHS and auxiliary port for video playing and recording, and optical disc and flash drives as well as floptical disk for computer removable storage. Airships use high-frequency and VHF radio signals. Airships also use photophone technology.
Satellites orbit the planet and transmit signals.
Airships also have defensive cannons and machine guns.
The captain has to turn the airship once every while. There are two people to take turns as captain, and a flight engineer and systems operator. There is also an autopilot, collision-avoidance radar, GPS, and alerts. There are small CRT screens and large, LED-backlit LCD displays.
Airships must avoid anticyclones that may suck them down.

Citations:

[2] Alternatively, medium-carbon medium-alloy steel (50% pearlite, 25% bainite, and 25% martensite). Alloy elements including nickel(5-12%), chromium(2-4%), manganese(0.4%), molybdenum(0.5-2%), vanadium(0.15%), tungsten, silicon(0.7-2%), sulfur (0.08%), phosphorus, aluminum (0.95%), boron (0.003%), copper(0.1%), small amounts of niobium, zirconium, calcium, cerium, and traces of bismuth and lead.
Otherwise zylon, Kevlar, fiberglass, basalt fiber, or silicon carbide fiber.
[3]Additives including ethyl-tertiary-butyl ether. Other additives include triptane, tetramethylbutane, ethylenediamine, and butylated hydroxytoluene), .
Other airships have E15 gasohol(with 10% ethanol and 5% isopropanol) homogeneous multi-port, 2-nitropropane(65%) and isobutylamine(65%) homogeneous direct injection, and 50/50 mix of UDMH and MMH(or alternatively Dimethylaminoethylazide) stratified charge.
[4]Otherwise, two-stroke V8. Supercharger instead of crankcase drives air into cylinder.
Or Wankel, RotationsKolbenMaschine, or LiquidPiston rotary engines. Fuel just 2-nitropropane(65%) and ethylamine(35%) direct injection.