I'm building a house on RCL right now and this sort of thing doesn't shock me. There is one house in my neighborhood that I'm sure had the exact same flooding problem about 8 months ago... To fix the problem, they constructed an extensive retaining wall and water catchment setup with a drain that empties into the lake. I think there have been others, as there are other properties with sketchy water diversion/catchment setups too.
It's the wild-west here. Most of RCL is unincorporated, but loosely governed by Navarro County and deed restrictions. Inspections by the county are minimal to none. I know they inspect the septic, but basically nothing else. The last time I checked, they only require the builder to sign a document that they have 'built the home to national codes'. <roll eyes>
If you are not familiar with basic building principles and assorted codes, you should not build a house out here without hiring your own inspector. Even the best builders here (which in my opinion, there are only about a half-dozen) do minimal inspections of their subs work... if you are not savvy enough to do your own inspections, or don't have the time, you need to hire someone to do it for you. While my builder is widely known as one of the top two builders in the area, I'm out at the build site nearly everyday overseeing. All the subs know me and ask me questions if they aren't sure what they need to do. I have run into several situations where I have either redone work myself or required the sub/builder to do it themselves. If I'm not sure about something myself, I educate myself and/or seek advice from experts. I'm recently retired, so I have the time to do this...I realize most folks don't.
Sorry to hear this happened to your parents. We did get an usually large amount of rain (3+ inches) in a very short period of time yesterday, not that it should result in something like this. Hopefully, your parents hired one of the better builders who provides a home warranty that is guaranteed by an insurance firm.
If your parents want a second opinion from some local 'yahoo' like me, I would be happy to take a look and provide my two-cents that they can take or leave. My dance card isn't very full right now, so it would not be a hassle.
