Mom offers a compromise

Your mother holds up her hands to both of you in a delaying motion.

"Now, now, both of you. There's no need to be frustrated." She interjected. Your mother failed to notice Andrea's eye twitch with anger and low growl. "Why don't you start with some common ground?"

"The fuck does that even mean?" Andrea asked, with a voice both tired and wound up.

"I mean, instead of both of you expecting the other to do the heavy lifting-"

"Are you calling me fat?" Andrea interrupted.

Your mother continued, ignoring her, "-why don't you each make a smaller effort to help eachother out?"

Staying quiet, both to avoid becoming a target of your sister's verbal mauling and let Mom elaborate, you continued to listen.

"John," Mom turned to you. "I know you're not comfortable being the center of attention or leading the charge, but your sister needs feedback on what you want and are expecting so she's not flying blind in this relationship."

The blonde in question crossed her arms under her massive knockers and looked smugly at you before your mother addressed her, "And you, young lady, John won't put much effort into this relationship if every interaction with you results in you biting his head off. He's new to this and won't be perfect right off the bat. Both of you are going to make mistakes, but this is going to come down to communication between you two. Give eachother some slack to make mistakes and don't be afraid to point it out as a learning experience, but try to understand that the mistakes made are not deliberately to irritate eachother. Does that sound reasonable?" Mom concludes her speech, looking between both of her children.

Nodding, you answer, "Yes, I can do that." to give her a verbal confirmation.

Andrea shrugs, causing her chest to jiggle slightly in her too-tight sports bra. "Sure. Whatever."