Advantage and disadvantage could be very loosely understood as a factor the Dungeon Master assigns when they believe it is appropriate. Players can and should justify why something would or would not grant them advantage or disadvantage based on events, but Fifth Edition leaves that up to the Dungeon Master to rule on. For example, if one were to leap upon a table and swashbuckle from it while kicking plates off it, the player could argue that they have advantage; after all, their character [i]is[/I] a swashbuckler and high ground would regularly give advantage.

While the Dungeon Master arbitrates such cases advantage is always applied, as with disadvantage, if the rules explicitly say they are. Thus some spells that grant advantage like [i]Faerie Fire[/i] always do. The only exception to this is if they would cancel out.

If you had two disadvantageous factors and one advantageous one, you would make a single roll rather than four. Advantage and disadvantage always cancel one another out despite how many there might be on either side; the result is always a neutral roll.

Hopefully that answers the first question I can help with, [@Mesonyx].