Having ladies of average size defend against an average man is a big ask... a lot of striking, grappling, throwing and joint locking techniques just won't work if the power ratio is something like 1:5.
A major decision for them is whether to learn an entire system of fighting as an art/style, or to learn a smallish set of specific moves as a compact self defence arsenal. If they do choose an art/style, I believe they should aim to find one that squarely addresses the self defence movements I list below, hopefully adding depth to the understanding of mechanics and application thereof, without too many other distractions.
Another factor is whether they aspire to learn to hold off an opponent who has time to pursue them, so they can't just get the upper hand briefly and escape to safety. That's hard - so much so that it's probably not worth the extra effort to learn unless they love the training for its own sake or you live in some particularly horrible place.
I'm not sure if this is what you're looking for as you seem pretty confident of your own understanding of combat techniques, but it's worth asking yourself whether your perspectives and training translate to smaller/weaker women vs. larger/stronger men scenarios, and to the need to get in one decisive hit without trading blows or being over powered. I'll make a list of techniques you might at least want to read over and cross-reference with your own impressions - feel free to ask me why I include specific techniques in the "recommended" or "not recommended list", or what I think about some other techniques.
A few suggestions:
do focus on doing a few things well - 95% of common techniques won't be effective against an average male assailant even if they're delivered well, so focus on the ones that can be. For example, these are worthwhile:
palm strike to the nose or chin
punch to the throat, chin, nose
slap across the jaw
forearm (thumb side) arm bar across the front of the face or side of jaw
forward horizontal elbow to the throat, chin, nose
poking the eyes if attacked with frontal strangulation
kneeing or front kicking the groin
there are others...
These are likely not worthwhile:
punching, chopping or kicking to the body (often ineffectual against stronger person)
kicking to the head (too hard to hit effectively - too easy to be taken down, and I say this as a taekwondo instructor now practicing kyokushin)
kicking to the thigh (ineffectual)
escapes from grabs/holds (the emphasis should be on striking well enough with the still-free limbs - while they're distracted with the attempt to grab - to get them to release and hopefully create sufficient time to follow up or escape, rather than narrowing the focus to match theirs; there are simply too many possible grabs to learn effective escapes for them all)
joint locking (very hard to use effectively against stronger non-cooperative opponents)
many others...
Something that looms huge in my consciousness for self defence and effectiveness of martial arts in general is sound body mechanics.
I'd particularly like to draw attention to the palm strike to the chin/nose:
fast and direct
linear strikes take more active timing to block than hooking swings where a blocking arm can just passively absorb the attack
most people's palms are pretty strong - there's a lot less chance of injuring yourself than with a punch where the wrist may buckle (or the subconscious may reduce power to avoid the wrist buckling) and unconditioned knuckled may be injured, though a palm can also be bent backwards too far is you hit closer to the fingers - there's still risk but less
palm strike can work very naturally to convey the power from the legs and hips to the target... it can be surprisingly strong
Some suggestions for developing a palm strike (for simplicity, assuming the right hand will strike):
practice "pushing" strongly against a heavy - even immovable - object, building that up to be a strong shove... once comfortable they can practice against your chest or shoulder and try to efficiently transfer their strength up through their legs and torso to move you backwards - the arm should be the last thing to add power - pretty much only after their leg has broken your balance and started you backwards
they adopt a stance alongside the "target" with the right palm near the right hip/ribs, just resting in a relaxed position touching the target, elbow backwards - the striking arm is kept tight in close to the body throughout - do not lift the arm like a swinging hook!
right leg back about one shoulder width and bent at the knee, rear foot fully grounded and turned outwards only a little (around 30 degrees - most people will want to turn it outwards further, and may need to stretch their calf to adopt this angle),
body rotated 45 degrees towards the target, and during the strike it rotates around the vertical central axis that runs down through the head and groin,
push with the back leg first, rotating the hips smoothly in a single horizontal plane without them lifting or falling, then as the right hip is forwards it should start dragging the right shoulder forwards, then the arm - still relaxed - gets dragged forwards too as the hip approaches the end of it's range of motion - a bit past frontal.
throughout, feel the torso twisting, and let those movements bring the hand forwards - the arm muscles can stay relatively relaxed and just twitch forwards during the conclusion of the movement.
The power in a good palm thrust comes up from the legs - the legs are doing something quite similar to a sprinter moving off the starting block - the bag leg is bent and ready to flick the right hip forwards - the shoulders and eventually arm are part of a whipping/chain movement, with the arm extension and strike itself almost an afterthought.
I've felt women around your wife's size deliver very surprisingly powerful strikes in this fashion (most notably a middle-aged frail lady who studied under the late taichi master Erle Montaigue).
Something else - some people have movements they're familiar with from sports - for example, one of my friends used to play volleyball and has a very natural, powerful movement for "spiking" a ball... while not ideal, using that to spike someone's nose is reasonable advice given that person's disinterest in spending time and effort to study proper martial arts technique. Similarly, look to use the physical abilities your family have... see if the movements they're already very comfortable and proficient with suggest any techniques.
