hmm. If using the same charger, on both phones, and neither will turn on, it sounds like the either the charger itself is not working correctly and needs to be replaced, or the battery is damaged/dead and needs replacing, or the charging port is damaged on both phone and needs replacing.
However, before going out and getting a new charger, try a different outlet. Just to make sure that isn't the issue. If it isn't the outlet then the cord being replaced would be next.
Obviously replacing the cord would be simpler, and cheaper than having to repair the phones.
Now, please note, since the phones are very drained/dead it is important to leave them charging for a few hours (versus a few minutes). Once most phones reach 0 or close, they...