You can get by with it, but you ought to consider other options. Who can be used on heifers but wasn't always failsafe, also remember both of your heifers trace back to him. The Shiver bull is working on heifers if you want an extra maternal kick. Ali will work, they aren't the stoutest in the world, but mostly easy coming out. An oldie but goodie is Payback even though he is PHAC he will sire great females and good saleable/showable steers.
Ditto! No Kadabra on the heifers. I would wait until they are 2nd or 3rd calf heifers before using Hannibal. Have you considered going Angus for the first calf. Your bloodlines are an investment. Gotta consider the heifer the first time, then you can go for what you want the next times.
Do NOT use hannibal on heifers....his calves are large (mine and others have been between 90-120) and they are SQUARE. Meaning they have big shoulders, and big hips....heard of the saying "round hole, square peg"???
There are better options, trust me!!!
My worst calving nightmare was Kadabara. We had used him on a cow and had a peanut of a calf. But, when AI heifers, my nephew mixed up straws and AI'd a heifer to him. C Section went bad lost calf and heifer the calf weight 150#s. Would never make that mistake again.
Northern Improvement for crossbred heifers you mentioned should work great. You are setting these females up for the rest of there productive life.