For the larger dog, it would need 0.07mL of the 1% ivomec liquid. Unless it’s a herding breed I would feel comfortable dosing that, although I would use an insulin syringe. (U-100 and draw up 7 units) For the smaller one its just too much of a risk, even if diluted but not mixed properly it could be deadly.
Some heartworm medications can be deadly if given to a dog who is heartworm positive, like Sentinel, which is why there is a prescription required. Also, in general, the general population of the USA is more likely to sue over a reaction that they should have known about had they read the package for a cat/dog type pet than for a horse/cow/goat. It sucks, but it is what it is.
Hope this helps!