Learn Farsi: دانشمندان این بیماری جدید را درمان خواهند کرد. - The scientists will cure this new disease.

To make a compound verb future tense, the conjugated helper verb خواستن (to want/will) is placed between the two parts of the compound verb. The non-verbal part درمان comes first, then the helper خواهند (they will), and finally the short infinitive of the verbal part, کرد.

Why does the object marker را come after جدید instead of right after بیماری?

The word را marks the entire specific direct object. Because the direct object here is the whole noun phrase این بیماری جدید (this new disease), the را must wait and attach to the very end of that descriptive phrase.

I usually see plurals formed with ها. Why does دانشمندان end in ان?

In Farsi, the suffix ان is used to make plural nouns for people or living things, like دانشمند (scientist). While you can also use ها for people, using ان is extremely common for professions and sounds slightly more formal.

If the subject was a single scientist, which part of درمان خواهند کرد would change?

Only the middle helper verb changes to match the subject. The non-verbal part (درمان) and the final short infinitive (کرد) stay exactly the same. For a singular scientist, it would simply be درمان خواهد کرد.