I think there's more to your sibling's taxes than property taxes. The data tell the opposite story - WI property taxes are higher than TX ones, at least if we look at the medians:

https://www.propertytax101.org/propertytaxbystate

As someone living in Fort Worth and making good money as a Staff SWE, I got a tax refund this year. It was due to paying interest on my house, but still.

I'd recommend asking your sibling see if they qualify for the homestead exemption, it's significant. You or they can check if they're using it and see their exact property taxes here:

https://www.tax.tarrantcountytx.gov/search