What is Sir Andrew's relationship to Sir Toby? What did Maria hear about Sir Andrew's purpose for being in the house? What does the presence of Maria and Sir Toby as characters imply? Who brings in a note of competition to this scene?

You need to enter each question separately rather than all at once. I'll take your first one. Toby Belch is crass and vulgar character who acts like his name sounds. He used his friends for his own gain and entertainment. In particular Toby uses and abuses his drinking buddy Sir Andrew Aguecheek. Sir Andrew supports Toby's bad habits seemingly oblivious or unwilling to accept the fact that he is being used.

To party together