Since he started with 30% in his little rant, I'll assume he's in either the 24% or 32% bracket, so making 100k/150k. He's self-employed, right? Health insurance premiums for the family and half his self-employment taxes come right off AGI.
Do they own that house? If so, they're young so nearly the entire mortgage payment is interest = deductible. Property taxes = deductible. State taxes up to $10k = deductible. (or its the property taxes capped at 10k, I forget; either way they're probably not exceeding that for either). Two kids = deductions/credits. A kid with a medical disability - Any of her expenses related to medical (including therapies, travel to/from, special equipment, feeding needs, everything) are deductions to the extent they exceed 7.5% AGI. Self-employment taxes on a gross of say $130k would be around $20k, and health insurance premiums have to be at least $1000/month for a family, so you're at 108k AGI. 7.5% = $8100, so anything spent on Luna (I'll bet they figure out a way to make 98% of her basic expenses characterizable as medical) not straight covered by insurance is deductible.
108k less mortgage interest, property taxes, state/local taxes, dependent deductions and credits, nevermind each of their business-related expenses* (or losses depending on where she is in her mlm, right?) ---> taxable income is now likely in the range ($42-90k) that would mean $4800 on the first $42k (11.7ish%) and 22% on what's above that (up to 90k, then 24% on the marginal amount up to 170k), so a blended effective rate of somewhere in the teens. And that's excluding anything special about their small business taxes/structures/filing strategy that benefits them.
*All his gym equipment, all their tech/electronics, memberships and subscriptions pertaining to their businesses, probably any woowoo stuff that could plausibly relate to her online stuff**, equipment, travel to clients, meals visiting clients, job-related qualifications/education expenses, maybe his car/truck if he uses it in the construction biz, maybe hers if she advertises on it, some portion of the home mortgage/utilities/etc - definitely the gym and office areas % of total house area, maybe more. Also, anything put aside into retirement funds is deductible up to very generous amounts (22.5k for an IRA, 60k+ for 401k).
* now I'm curious what people who make money with online "lifestyle" presences/personas can legitimately deduct - seems potentially a TON, provided they're actually making money.