Valium is certainly a case in point, as it is very easy to administer an overdose, so it is best avoided.
Seroquel is dangerous too, as it is primarily used as an antipyschotic in humans
and is unsuitable for dogs (one effect being an increased risk of cataract in dogs).
In short therefore, do not use these drugs for your dogs. If possible, take them out for a good walk or run, and this will almost certainly calm them for the rest of the day.