Cod liver oil is not rich in long chain omega-3s, it's fish body oils you want. I don't recommend supplements to my nutrition clients as a matter of routine, only to fill in unavoidable gaps or where playing 'catch up' is needed for a likely deficiency, I always advocate wholefoods. What is it that hubby doesn't like, fishy burps, size or number of capsules? You can purchase no fish flavour capsules, triple strength capsules, fruit flavoured liquid, always have before the largest meal of the day so they are digested quickly.
Seborrhoeic dermatitis, atopic eczema and acne are all inflammatory conditions, so it might be worth generally overhauling your diet to be anti inflammatory.
Ideally have your entire family eat oily fish itself, they would benefit from the other nutrients it contains including bioavailable vitamin D, some of the B group and various minerals. Many seafood items are superfoods that humans evolved eating on a daily basis. Possible recipes: Asian style fishcakes, homemade fish fingers, fish pate made with soft cheese and canned sardines or mackerel in tomato, fish pie with hidden veggies in the mash topping. The oilier the fish the stronger the flavour but the smaller the serving required - being 'delicate' salmon and trout are often best accepted as a plain fillet of fish. You can also get hold of omega- enriched eggs which are a useful family friendly add in.
Castile soap is pretty awful for skin, it's highly alkaline so decimates the protective acid mantle and skin flora, strips structural lipids from the stratus corneum. It's not even that natural, it's made by chemical reaction in a factory from corrosive lye and was never intended for personal hygiene. Soap was invented as a degreaser for fabrics like wool and household items - basically early dish soap and laundry powder. Because it destroys microbes so effectively it can clear up some skin complaints, but as soon as you quit they can come back with avengeance.
Better alternatives are surfactants like the glucosides or betaines in a product that is pH 4.5 to 5.5, if you like all natural I believe soapwort extract and soapnuts are on the acidic side and have been used by humans since the stone age. SLS is far from the only nasty many of the anionics are, it was SLES shampoo bubbles triggering my eczema, the olefin sulfonates are highly irritant too.