Re: Need Information: Sealing a concrete slab to house framing
I can't give the citation, but I think code requires a 2" minimum step on an exterior patio to the interior floor height. This is to prevent water running inside under the threshold. You can have a ramp, however, to facilitate the "Universal design" aspect.
Heed the above warning about properly isolating the wood sills from the masonry; we usually use copper flashing over Ice & water shield brought up the walls, so melting snow drifts won't seep in behind. The wood siding should be at least 2" above the patio floor so splashing of rainwater can run off. We leave that as exposed copper, which ages dark and looks unobtrusive.
Remove not the ancient landmark, which your fathers have set.