Hello I have gone through your question and understood your concern. The blisters on your father s shin can be a symptom of water retention (also known as fluid retention or edema) with the appearance of chronic diabetic skin blisters. In diabetics ,the blisters occur on the outside surface of the body and cause raised areas filled with liquid.For this reason it is very very important to take regularly the water pills. If the blitsers broke,like in your father s case,it is very important to keep the clean,apply an antibiotic,cover the wound,change the dressing and watch for signs of infection like redness and pain. Diabetics are more prone to infections and the wounds are slow to heal. -In my opinion you should seek medical attention and treatement for your father because the blisters can produce dangerous compication like staphylococcal infection( that sometimes leads to amputation), bone infection near blister sites if blisters are recurring and ulceration of blisters,if not treated adequatelly. Hope this is helpful. If you have other questions,feel free and ask. Regards.