Handwriting

My three oldest princesses are right-handed.  All three of them hold a pencil in a very unique way.  (That's a nice way of saying I don't know how the heck they can write that way!)  My DH has a pencil grip very much like Princess E's grip.  Her's looks like this:

She can write beautifully IF she writes slowly.  You can't really flow very well with a grip like that.  I tried to correct it, but when I realized that she holds it like her Dad, I figured there was nothing I could do - that it was an inherited tendency.

Then there is Princess S.  Princess S - I believe - has some SPD issues.  She has a hard time writing anything.  She loves to draw, however, and is quite talented at it.  But her pencil grip is very ugly.  And it's no wonder that her hand gets tired after only writing one sentence.  Get a load of this:

She very much dislikes her writing.  It is the epitome of chicken scratch.  And I know her grip is part of the problem.  But fixing it is near impossible.  Any suggestions?

I have put a specialized pencil grip on Princess L's pencils in an effort to force her to use a correct grip.  But if left to herself, then she has a grip like Princess E's.  I'm not sure how picky to get with her during school when she goes back to her own way the rest of the day. 

Princess M is a lefty.  And she holds a pencil correctly.  Go figure.