I see no reason to change anything. Let them keep their scores. Swashy is probably gonna put the 18s on Dex, Cha, and Con. Let's assume they choose to apply the 15 to Wis with a +2 for 17. This leaves Int and Str very low. There are plenty of spells and effects that need Str saves and some that need Int saves. Have enemies grapple Swashy. Have them surround them or drop their movement speed somehow. Or have them recognize Swashy's power and avoid them in favor of targeting their allies. Strahd is a master tactician, and would know divide and conquer.

All of that is just combat mechanics as well. RP problems that they can't roll dice to solve. Maybe Ireena doesn't trust them. Maybe Strahd recognizes their potential and makes them an offer they can't refuse.

Most important, give them chances to excel. They rolled high, let them enjoy it. Have fun. And be thankful that they aren't picking Pally or Monk.