双方は英語で
both

英語の定義

双方
1. n. both sides, both parties

both
1. det. Each of the two; one and the other; referring to two individuals or items.
"Did you want this one or that one?" — "Give me both.".
Both children are such dolls.
2. det. Each of the two kinds; one and the other kind; referring to several individuals or items which are divided into two groups.
3. conj. Including both of (used with and).
Both you and I are students.
4. conj. (obsolete) Including all of (used with and).

bilateral
1. adj. Having two sides.
2. adj. Involving both sides equally.
3. adj. (of an agreement) Binding on both of the two parties involved.
4. adj. Having bilateral symmetry.
5. adj. (anthropology) Involving descent or ascent regardless of sex and side of the family.
6. n. A meeting between two people or groups.