Basically your question is what CC offers the best OneWorld miles bonuses, right?

- earning points/miles on a CC based on purchases would be moot since your folks would have to spend potentially $40K a year just to get enough for one US-Hawaii award.

- Have them apply for a Chase BA Visa. You can search on Flyertalk for sign up bonuses from 50-100K which will give you enough tickets for OneWorld partner awards on AA. Beware minimum spend to get points currently can be high.
- AMEX Plat bonuses from 25-50K, and now with transfer to BA Avios at 150% for a limited time.
- Citi AA Card gives bonuses as well 30K to as high as 75K. Depends on how lucky you are and when they offer these cards. I believe the best offers right now are 30K
- Alaska BofA gives limited sign up bonuses but gives you OneWorld and Alaska options to Hawaii
- If your parents have a significant nestegg of retirement cash , then have them deposit up to $200K into a BankDirect account and accure 240,000 AA miles annually just for keeping the money in there. $12/month account fee applies, the money earns negligible interest but the value of 240K miles is spectacular for redemption(6 RT continental US-Hawaii tix/year), and miles/value of miles are non-taxable. Similarly if they only travel once per year as a pair, keeping 80K in the bank each year would yield two HI tickets/year on AA.

Good luck.