It is best to visit Shimla and Manali with family during the months of summer between March to June as the weather is pleasant on this time and making sightseeing and outdoor activities comfortable. If your family enjoys snow then visiting between December and February can be ideal choice for experiencing snowfall and winter sports. Consider booking a tempo traveller on rent in Delhi. It would be suggested to pre-plan for which places you are going to visit and how you are to travel to avoid last minute hassle with family.