We are in the process of buying a DVC ownership. I have researched over a year before we decided to purchase. As far as the VGC goes, there are only a small number of rooms available for DVC owners. Demand is VERY high from what I've read and getting a reservation at 7 months is difficult. Go to the rental board on the DVC sections of DIS. You can't post what you want, but you can reply to peoples posts about available points. Your goal would be to find a renter who OWNS at the VGC, although I have NO idea how easy this would be.
I can tell you the standard rental is about $11 per point. You may find some for $10. That has been the standard amount for the past few years, but with dues increasing each year, the prices are going up for rentals. You can find points for less but they are points that need to be used ASAP or the owner will lose them, and that is NOT going to be ideal for a stay at VGC.
You can't check prices for the VGC on the
Disneyland website, as they are only booking through DEC 2012 right now. I did a quick check of prices for early Nov, and it's $395 for a weeknight, and $460 for a weekend. Points at $10 would cost you $310 and $400 for the same dates, but your room WOULD be bigger as a 1 br DVC room. A much bigger savings on the weekday.
I wouldn't put a lot of faith in being able to rent for VGC in Disneyland. Renting is a much more viable option for WDW as there are over 3000 different rooms vs 71. Another option for you is to try David's Rentals. Google them. They rent out points FOR DVC owners, and you are much more likely to be successful in getting what you want, but they also charge $13 per point, with $10 going to the owner and they take $3 for their service of doing all the legwork in securing reservations. However, at $13 per point that's $403 for a weeknight, and $520 for a weekend. Not going to save you any money.
I would recommend renting points if you travel to WDW, but not Disneyland. Unless there is some reason you HAVE to stay at the Grand Californian. You will do much better booking through Disney directly, or staying at another hotel.
EDIT.... Just reread your first post and missed the part of needing 2 rooms if booking through Disney. They will allow you to stay with 5 in the regular room (I just tried to book with 5 people, 2 adults and 3 children, and it didn't give me a problem). Just providing you some info.