Lack of fiber can definitely
If you're making mashed potatoes, keep the skin on and limit the butter, salt, sour cream and cheese that a lot of people slather on. A little chicken broth (get the low salt - Swanson makes a pretty decent variety) can go a long way to add flavor without also pouring on calories and fat.
Other veggies - broccoli, cauliflower and other root vegetables are good; we always have both in our house. Broccoli is often a hard sell for children (a lot of them find it bitter), but cooked, pureed cauliflower may work; just mix it in with mashed potatoes. Salads, too, or raw vegetables with dip. Carrots are great; snow peas can be fun. Experiment with new varieties, and see if you can get out of the potato/plain salad comfort zone.
Also, ethnic foods can often be better - e. g. try cooking Asian one night per week or every two weeks. As in, brown rice (it's got more fiber than white), mixed Asian vegetables (you can use frozen if you're pressed for time) and a smaller amount of meat or fish, sliced into strips, and not too much sauce. Mexican is another option - beans have a ton of fiber (yeah, there will be gas); add brown rice again, mixed vegetables, a smaller amount of meat or fish, again sliced into strips and add salsa - maybe skip taco shells and have it all over a bed of romaine lettuce (much better fiber content than iceberg lettuce).
Go with breads that are pretty much any color other than white. Cereals - check labels, look for over 3 gm of fiber per serving. Oatmeal is a great option; just add fruit for variety. We also add flax seeds (I buy them in bulk from Amazon, of all places).
Consider changing the proportions on everyone's plates. When I was growing up (I'm 50 now), it used to be that your plate would be about 1/2 meat, 1/3 starch and the remainder (1/6!) was vegetables. Fact is, it should be a lot more like 1/4 to 1/3 protein (not necessarily meat), 1/4 to 1/3 starch and the remainder 1/3 - 1/2 vegetables.
And - this is really important - make sure everybody is drinking water. The transition to a higher fiber diet can also cause intestinal distress, but water helps (it gets everything moving; 'nuff said).
It's a change, and not everyone likes change, but I think your husband in particular is seeing that it would be good to switch things up. BTW, eat like this and the likelihood is not only that your gastrointestinal issues will be reduced if not eliminated - you might also find yourselves with lowered cholesterol and maybe even lower weight.