First you need to make sure you are using RG6 wire since the old wire has to much loss for the digital signals.

Do not atempt to use a old signal amp they often have to much noise for the digital signals.
The main problem is most likely in the UHF signals make sure that you replace all of your splitters ones rated for UHF. It would be better if you could find CABLE TV drop taps to use in place of splitters since you need 35 taps.

Try and see if you can find someone that has a cable tv signal meter so you can tell where your signal is going down.

You can also try preamps at each TV but thats a last resort and should not be needed if its setup right.



Here is another option. The one I would most likely take on a 65 room complex that you do not want to rewire.

Build your own cable tv headend. Take a convertor for each ch you want to receive and tune it to that ch and then connect its output to a analog modulator. You can then convert all your digital channels to analog VHF ones and it will work with your existing wiring and amps but not be in HD.
You will need to use convertors that reboot to the last ch viewed in case of power loss. Suggest the dish settop boxes.