As compared to Elvis, Lea had a higher tolerance towards alcohol and Elvis was stronger than Lea so when Lea's drunk, at least there's Elvis present to suppress him. So, after a discussion, both of them decided to let Lea try the wine while Elvis should not touch a single bit at all.
Gu Mengmeng said that there's actually no need to do that because there's only a few barrels of grape wine. Currently, the available grapes were only the small amount at the stray beasts' camp. And Peter was not the stray beasts' leader anymore, it was not as easy as before to pluck grapes at the stray beasts' camp so Gu Mengmeng still wanted to save the grape wine she had and drink them carefully.
Since Elvis and Lea were not good at drinking wine, they should not force themselves because she could drink all my herself, gosh!