Daniel lie said:

Hello everyone,I'm new to the forum.I have a few questions to ask.

Welcome! 

Daniel lie said:

1.How to accept a friend request? I can send requests but I can't find the tab where I can accept.

That is a part of Plarium's portal, so outside of the game. Look in the top right corner:

Daniel lie said:

2.When I visit my brotherhood members' Haunted Cemetery,I can't click it to summon a corsair.Am I doing something wrong? Thank you in advance.

First, DCs have nothing to do with your brotherhood. They are tied to your friends.

Second, if you visit your friend's haven, you might be able to click their cemetery to summon your DC for them, but if they already have your DC, you won't be able to do so (which makes sense, as there is nothing to summon). Once your DC that they have dies, you'll be able to re-summon him (unless they summon it themselves).