Have you candled the remaining eggs? What I do with overdue eggs is to hold them agains my ear and tap them with my fingernail. If there's a live chick in there it usually responds by moving around, cheeping or tapping back. If I don't get a response I very carefully shake the egg, to see if it...
First of all, read these threads:
Incubating & Hatching Eggs Important Topic Index - Please Review
There's an excellent thread there on helping chicks hatch which helped me enormously!
The lower incubation temperature could've caused the chicks to develop slower, so don't toss the unhatched...