Apart from the special lam in the divine name, an ordinary lam is generally pronounced lightly. It is not automatically made emphatic because a nearby consonant happens to be heavy.
«مَا لَهُمْ» — ordinary lam is light.
«وَكُلِّ» — do not introduce heavy lam.
In «اللَّهُمَّ», the lam of Allah at the opening has its special heavy treatment. Its doubled final mim involves a separate rule of nasalization, developed in the subsequent lesson.