Hi. Basic RF physics are that lower frequencies penetrate more obstacles, propagate and 'bend' around structures more, and higher frequencies are blocked by obstacles more and even attenuate through the air more.
So, that's a double edged sword - higher frequencies tend to have better fidelity, less interference - plus higher frequency antennas have higher gain in a give antenna size. Lower frequencies tend to penetrate better, but also pick up more interference from the neighbors router (which is also penetrating everything more) and the same size antenna will have less gain.
To extend that example further, if you go down to 900 Mhz, that's better at penetrating trees.... or is it? Because a 4' long Yagi antenna is only 17dbi gain, whereas that same 4' Yagi would be about 24 dbi if it was at 2.4 ghz and it would be about 28 dbi if it was made in 5 ghz. The spacing and length of the elements would also be different of course, but the point is - that in 900Mhz, a point to point link would have 17 + 17 dbi of antenna gain, while that same link with the same size antennas might have 24 + 24 db of antenna gain. In some cases, the lower frequency will penetrate trees better, but in some cases the more antenna gain will more than make up for the foliage attenuation. Every environment will vary.
So - to answer your question about inside buildings - no, 5ghz will not penetrate walls better. 5Ghz will be blocked by walls more. But, that can be a great benefit. That's exactly why 5Ghz is cleaner and faster and less congested too. So, where it does reach, it'll be faster and more interference free. But, 5Ghz typically won't even penetrate everwhere in a moderatly large house. So, in an office environment, you likely need to install several routers spaced around to give the proper coverage, but since the walls block the signals so much, every router won't be competing and interfering with all the other routers either, and the whole network can be much faster as a result.
the 5ghz constraint and restriction from the attenuation can be a great tool. we recently did a school with an AP in every single classroom. power turned as low as possible so each room is served individually, now that school is getting we over 100mbps to each class room without interfering with a neighboring room, absolutely no dead or even weak spots in the building from that deployment method, and thanks to the characteristics of the 5ghz signal, no noticeable self interference
in your situation, 5ghz could be used to provide HD service to every room without impeding guests performance really easy. you will need to deploy about 2x as dense as the 2ghz at a minimum, however you'll have many times the capacity and far less dead spots. remeber to reduce the TX power of the 2ghz side of your APs when you do that, having them at full power will make your 2ghz side of the network almost unusable when its busy.