Hi,
sorry for late reply.

Is there a way to force user to accept our policy befor sign in (for the fist time) with social login?

Yes, but is not simple, we will add this feature to our TODO list.
For now you can do this:
- Create a usergroup named "Pending Terms"
- Create a Access level called "Terms" and set these groups "Guest" and "Pending Terms"
- Set the "terms of use" field with Available for "Terms" accesslevel
- From Easy Profile option set to add user on usergroup "Pending Terms"
- From Easy Profile option set "Force the compilation of the required fields on login" parameter on Yes
- On "terms of use" field set this condition:
if not equal to 1 add to "Pending Terms" usergroup

Now when user register your account with normal registration, he will have "terms of use" field (because the user is guest on registration)
When a user register your account with social network happen this:
- User will go on "Pending Terms" group
- User will have "terms of use" field not filled and required
- When user log-in will be redirect on edit page (because he have a required field not filled)
- When user fill "terms of use" field, it will removed from "Pending Terms" group

Another question for user who has got a previous account on my website. Is where a way for their to link their social account to not create a new account when they use social login?

Yes, if email is already registered our plugin ask credentials to link Social Network login on existing user. Or if user is logged in the button of Social Connect plugin become button to link social login to current logged in user. To render this buttons read here https://www.easy-profile.com/docs/24-social-connect.html