How do you deal with swarms or tanky two ship builds?
I am not a rebel player, so I don't have their full reportoire at my fingertips, so I might miss one or two solutions...
Swarms usually revolve around a key ship, like Howlrunner in the T/F, Serissu in the M3-A or Epsilon Leader in the T/FO, that ship usually defines most moves of your opponent as it's effect is what they want to use most. It is this ship you have to take out at earliest opportunity but not to the point that you don't take their ships of the board.
And since Swarms have a rather good board control with their many ships and spread out firing arcs, it is best to avoid concentrated fire and see that you can split them up, so no single ship of yours is ever in all enemy firing arcs at once. Most swarm ships (T/F, Z-95 etc) have only 2 dice when it primary firepower, so keeping your focus for defense might be advisable and try not to get caught in Range 1.
Two Tank Ships (we are talking Brobots*, by any chance?) are very tricky cause there are many permutations of those to which not one solution applies. But with an opponent with a low ship count, blocking is a useful tool; Blocking is purposefully putting one of your ships into a position where you anticipate your opponent to move a ship to before they move, Swarms excell with at this due to their in-build redudancy and low pilots skills. Since you have a low ship count and high pilot skills yourself that is not feasable for you.
If blocking can't be done, remember that the golden rule is "not being shoot at > shooting yourself", try to maneuver and position yourself out of the firing arc of ships that can only use their primary arc to fire. If you are dealing with ships with turrets it depends on the kind of turret: Primary Turrets (YT-1300, YT-2400, VT-49) can be held at bay by staying away, while Secondary Turrets (Y-Wings) must be taken out at close range to maximize your primary weapon dice. In any chase you should try to maximize your defense dice through the use of obstacles and range (if applicable).
YV-66 and the Firespray are a different kind of animal all togethee: with YV-666 you will most likely face a more stationary vessel as it can do the speed 0 move and that way maximize it's board coverage but that makes it predictable and slow. The Firespray is one of the hardest ships to "arc dodge" (= staying out of the enemy firing arc by maneuvering) since it has only 90° blind spot at either side but that is usually just a matter of training to get that right.
*Brobots = 2x IG-88 in any combination with the IG-2000 title
EDIT: Another tip: Use the rules to mix and match your obstacles, if you are so inclined - in competive play you register 3 obstacles of your choice along with your list for an event, which you have to use in every game (giving you a total of 6 when your opponent brings 3 of their own). This allows you to pick 3 obstacles that work best for your list or hinder a combination of ships you have problems with.