If your line of sight is over the top of the trees, it is very unlikely they will do the install. Trees grow, so in a year or a few years, you will lose your line of sight.
They won't actually do the install to test it though. The installer will assess the line of sight visually (possibly using compass and/or inclinometer) and decide if line of sight is there or not.
You mention Tivo. You have to decide whether you want DirecTV's normal DVR and receiver system, which accommodates whole-home (you can watch recordings from a DVR on another DVR or receiver), or if you want the Tivo based DVRs (which are not able to do that). If you want the whole-home capability, then you need to go with the HR2x DVR or HR34 home media center. If you want Tivo, then you need to get a THR22 Tivo based DVR for each TV location. Place your order accordingly.
They won't actually do the install to test it though. The installer will assess the line of sight visually (possibly using compass and/or inclinometer) and decide if line of sight is there or not.
You mention Tivo. You have to decide whether you want DirecTV's normal DVR and receiver system, which accommodates whole-home (you can watch recordings from a DVR on another DVR or receiver), or if you want the Tivo based DVRs (which are not able to do that). If you want the whole-home capability, then you need to go with the HR2x DVR or HR34 home media center. If you want Tivo, then you need to get a THR22 Tivo based DVR for each TV location. Place your order accordingly.