You can easily do all this in 4 days , just start exploring from bhuntar take a bus to malana , kasol, manikarn, tosh you can stay 1 day each place d explore easily..
It's very much possible but I wouldn't recommend that .You can do kheerganga in a day but it'll become too tiring at the end of the day .To reach Tosh , you have to reach Barshaini by bus and Trek for about an hour . Kheerganga starts from Barshaini too.
Good Luck!!
Kasol, malana, tosh are at walking distance and on the other hand banjar, jibhi are at walking distance from each other and kullu is the nearest major station so all these sites can be easily covered in 3-4 days.