8老師, to answer your questions:
1). My spouse has 2 yrs combo card valid till 2015/4 and child has 1 yrs combo card valid till 2014/3.
so it was kind of wired for them both to get same I94 card expires at 2014/8.
-That is a parolee I-94, and it is normally for one year. But it does not matter to you to stay in US even if the I-94 expires.
BTW, since my family have used AP, are they still on H4?
-No. They can reinstate their H-4 by renewing it any time if they want to.
Do they have to renew the EAD combo cards before the cards expiration dates to keep legal status?
-Not necessary unless they want it for travel again.
2). Actually they got I94 at Seattle airport.
-Fine for the paper I-94.