"On vous écrit tous" is "We all write you". It means that either just men or men and women are included. "On vous écrit toutes" is "We all write you"; however, this time, only women are included. "On vous écrit tout" is "We write you everything". It can either be just men, just women or men and women included. On nous aide tous= We are all being helped. On nous a tous aidé= We have all been helped. Je vous écoute toutes= I'm listening to all of you. (Only women) Je vous ai toutes écoutées= I have listened to all of you. (Only women) On vous écrit tous= We all write you. (Just men or men and women) On vous a tous inscrits= We have registered all of you. (Just men or men and women) On vous a toutes inscrites= We have registered all of you. (Only women) Hope that helps.

Beni is right regarding the translations, but what's even the meaning of this precise sentence (and the following "On vous écrit toutes.") Doesn't make sense to me. Is it something like "We all write" "On écrit tous" and then "On vous écrit tous" "We all write to you."? I don't know, isn't really common though.