"Be friends with..." is correct. You can also say, "Be a friend to..." This means "act as a friend". Example: "Be a friend to your friends when they need you."

Be friends with somebody - correct Be friends to somebody - incorrect :)

As Abdullah says. be friends with ... is the frequent use. . Be friends to someone is a less frequent, form that means help them in some way. Be a friend to him, give him a ride home, this once. . Both are normal uses. Just different meanings.