The high 40's, but if you want to be safe, get them in the 50's. Make sure they all know strong moves. You will definitely need a level 50 dragon type, to take care of the champion.
Good luck!
level 100 i am shaqib and i beat heartgold, dimond, platinum, black, white, all of them actually .
The elite 4's Pokemon the first time you beat it the level range is 40-55. After you beat all the gyms the level range is 50-75.
train your pokemon up to level 80,90, or 100 and teach it TMs and HMs
Mount silver, or the elite four (With exp share.)
On Pokemon HeartGold, Moltres is on level 50.
Kill? hehehe...If you really wanna do that,you are in the wrong game,but if you want to just defeat them,then level your Pokemon more :D. 70 Level should do the trick.
your Pokemon sould be at least a level 25
they should be lvl 55-62
50 and over.
You can get a level one hundred Pokemon in HeartGold the same way that you can get a Pokemon of that level in other games. You have to level them up until they reach it.
For the first time at least all Pokemon should be level 55 or higher.
5-100