Paying someone to take care if your dogs for months at a time is probably gonna be more expensive than traveling with them.
The cost breakdown for ROUND-TRIP between the mainland and Hawaii:
$1,700 United Airlines pet-cargo (dog+kennel, cat+kennel)
$ 330 Hawaii quarantine direct-release (x2 pets)
$ 500 Vet check-in at airport (x2 pets)
$ 200 ~Vet checkup/paperwork before returning to Hawaii
The daily rate for a pet-sitter to come to my condo for 30-minutes a day to walk/feed/play is $21 for x2 pets.
This works out to 130 days for the break-even, or IOW, 4 months. Anything over 4 months and I'm better off cost-wise to brings the pets with me. Under 4 months, cost-wise the pets are better staying in Virginia.
But no way I want to be away from my pets for that long, so I'm saying 2 months max. If I can, I will try to only be away for 1 month at a time, 4x times a year.