A1. Yes they will help achieve CFW
A2. You should be to get CFW on both PSP's using a hard modded phat battery, I am not sure if a hard modded will work with a Phat PSP, but I dont see why not.
A3.What do you mean by risk, the PSP's wil not be damaged if the battery gets messed up, just the battery it self. If all goes will, there is a low risk, if you follow all steps when in staling CFW.
A.4 You cant update to OFW if you have CFW running, we simply wait for a new CFW to be released.
5 Don't forget a competition running to win a Slim Battery tool, read via this
post
Hope this helps