The fist sentence uses both adjectives in the feminine form, while the second uses both adjectives in the masculine form (providing information about the speaker), so you can't mix those up.
So are you saying that the gender in this instance is determined by the gender of the speaker and not the gender of the group as a whole, like when using the word ei is all males or both male and females, where as ele is only females.
Yeah, my answer was confusing. You're right, it's about the group, not specifically the speaker. If it's all females, it's "scunde și grase", otherwise it's "scunzi și grași".