Let's talk this through and come up with an agreement
Please don't make all the rules onesidedly =一方的にルールを全部決めないで下さい
onesidedly =一方的
one side =片側、から来る形容詞です。
Let's talk this through and come up with an agreement =これはお互い納得行くまで話し合おう
talk this through =(納得行くまで)話し合う
agreement =契約、合意、一致