Yes all your dogs weigh less than 22lbs they need 1 tablet each and your dog which weighs 82lbs needs 3 tablets.

Drontal protects from tapeworms for about 3 months. You need to give 2 tablets every 3 months.

Each tablet for 10 kg of weight. So if your dog is ≤10kg you need to give him 1 tablet, if ≤20kg 2 tablets, so on.

NG Spectra covers most of the usual intestinal parasites too. Unless there is a risk for tapeworm or some other specific worm that NG Spectra doesn't cover, then you don't need to use Drontal or any other de-wormer if you use NG Spectra.

Yes, you can combine Heartgard with Drontal no problem.