Both Hepatosupport and Vetri-DMG can be given with food and at the same time if you want...no need to give on an empty stomach.
Yes, you give hepatosupport and vetri-dmg OR hepatosupport and denosyl
I would start out with less and build your way up to the proper dosage.
The recommended dosage for dogs less than 25 lbs is 0.5 mL daily.
If it were me, I would start out at 0.125 mL in the morning and 0.125 mL in the evenings. Then, work your way up to 0.25 mL twice daily.