No idea in KM but it is an easy trek. Last stretch is a bit narrow and steep otherwise rest is quite manageable easily. Its a trek of about 3 hours with medium pace.
Ponies were costing 1000 in 2011, don't know this year's price.
If you own the camp, they will charge you 200-250 per camp to pitch it in their premises. If you use their camp then its 700-800. If you get the hut, it is 1500. The best one is Raikot Sarai
I haven't visited with family but I plan to in coming summers. Visiting with family is no problem at all at FM.