The most likely explanation for bruises could be
Associated consumption of some anti coagulant or aspirin
Wrong method of injecting insulin
Talk to your doctor and learn from him the exact method of injection
Don't rub the site after injection.
Let the alcohol from swab dry before giving injection.
Always use fresh needles.
Press the site immediately after injection.
Don't use the bruise site again till the bruise subsides.
Keep rotating your site.
If these measures don't improve your problem get your father investigated for bleeding and clotting disorders.
He must stop eating sweets as this can land him up in any emergency any time.
He already had these emergencies in past.