Thanks for the query
1) Yes, you can use it upto 6 times a day. Its a plane saline drop so it will nit cause any harm. Be careful while instilling the drop, never use saline in both side at a time, put first in one then after 1-2 mint. in other one.
2) Passing 6-8 stools in a day or once in 5-6 days is normal for this age. Rule out any thyroid
problem by consulting your pediatrician
3) If any one in family is suffering from cold
he or she should stay away from the baby. But as you are mother it is not possible, so avoid direct exposure by using face mask if possible and get your early treatment.
I hope this answers your query well
Wish you and your family good health