I presume that the gr^ha or griha (not "graha" which means planet - navagraha) is to be done on 30/9. If so it is mandatory that all the inmates of the house, including children sleep on that night in the new house and take some food there next morning also. If this is not done life in the new house will be highly unsatisfactory, it is generally believed. Even for occupying rented houses these are followed. This requirement is more important than Mahalayam and pitru prasaadam etc. Of course if kuladeivam is known some amount can be sent to the kuladeivam temple on the grihapravesam day or earlier.Madam,
can you move your household things only to the new house on 30-09-2010,and can you stay in a lodge or hotel or stay in your friends house till 9 -10-2010. Some group of people is adopting after amavasai each month as next month (aippasi)i.e for this month. It is better to do mahalaya srardham before going to the new house. mahalaya paksham starts from 24-9-2010and ends on 7-10-2010. Request your father in law to do mahalayam before 30-9-2010 and abishekam and archanai to your kula deivam and some contribution to the kula deivam temple.
First preference should be given to the pithrus and then only all other poojas and ceremonies should be done and during navarathri poojas you will have no time for shifting household articles as in olden days they will do special poojas during navarathri. This is the simple reason in olden days they avoided puratasi month. Then once again milk boiling must be done on 9-10-2010.