Better would be to try to reach Sharda as you have just 4 days. Leave early if you can, like after fajar prayer, 4 am. You should be in Muzaffarabad by 10 am. You can take brunch there and set off for Sharda. If you leave for Sharda around 12:00 pm then you can reach by sunset. Night Stay in Sharda.
Leave early like 7 to 8 am and go to Kel. This 21 km can take 2 hours if you will go on your car. Drive slowly and with patience. Arrange a room in Kel, put your luggage and go to Arang Kel. It would be really difficult trek for small kids or some older person. So if you have parents with you then they can stay in hotel. Dedicate this whole day for Arang Kel. Arang Kel achi trah tassalli se phirnay vali jga hai it deserves a lot of time. Wander around here and there and try to reach forest on the right side of the Arang Kel which will come after crossing all the village and fields. Spend whole day here and spare just 1 and half hour for descending back to Kel before sunset. Night Stay in Kel.
Leave from Kel for Keran or Upper Neelum (I mean Upper Neelum village which is situated at Keran, I am not talking about Upper Neelum valley which is Kel to Taobut).
Don't leave early this day because after staying in Sharda and Kel, you may find it hotter in Keran these days. So try to reach there after the afternoon like 3,4 bjay.
Night stay at Keran or Upper Neelum. I would prefer staying in Upper Neelum over Keran. You will have a wide view of the whole Keran area. You will see AJK on one side of the river and indian occupied Kashmir on the other side. Also weather would be bit colder in upper neelum.
Spending last night in Keran will make you face less travel to get back to home. You can leave in morning aram se nashta kr k and you will be home inshaAllah by sunset.
The only problem with above plan is that all three nights are in three different destinations. So a lot of packing unpacking, loading unloading etc. More the points/destinations to stay, more the hassle.
To avoid this, you can even spend all three nights in Sharda and leave for home from Sharda on Day 4.
But for that you will have to get back from Kel to Sharda on Day 2 after Arang Kel activity which will be tiresome for everyone and also you will need to manage time really tightly like leaving quite early from Sharda for Kel.
But believe me, "staying at one place and day trips to other places" has its own advantages. It saves a lot of time and hassle.
There can be many variations, like 1st night in Keran, 2nd in Kel and 3rd in Sharda. Or 1st night in Keran, second and third in Kel etc etc. You can do whatever suits you.