What are the difficulties that bilingual students face while teaching a new language? how can they overcome these difficulties?

The major difficulty faced by a student in learning a new language is the ability of the student to comprehend the questions mainly caused by cultural differences where the student may get confused in trying to communicate with the speaker. 

There are various teaching methods to overcome this difficulty, for e.g.

AUDIO LINGUALISM - Role Plays, Interactions etc

PRESENTATION, PRACTICE & PRODUCTION - Videos on Target Language, Work Sheets.

TASK BASED LAERNING - Task and real-life situations which are closely associated are presented to the students.

COMMUNICATIVE LANGUAGE TEACHING - Highlights the essence of environment, Engage students in interactive activities and so on.

COMMUNITY LANGUAGE LAERNING - Students decide on the aspect of language and what they want to learn,  Not class but Group, Students choose the topic.

The Silent Way - Teacher speaks little, Learners speak and discover the language rather than memorize,  Use of physical objects for easier learning, Problem solving tasks etc.

Apart from these very popular methods there are several other approaches that the teacher may resort to depending on individual circumstances like environment, culture, personality etc.

However there are a few methodologies (given below) that have a proven track record in overcoming the difficulties of teaching a new language :

Students need maximum exposure to language

Inputs from teachers is essential

Communicative tasks though effective is not enough

Anxiety and stress for learners needs to be low

Encourage students to discover language for themselves

Vocabulary is as important as grammar

Integration of methods is the best approach

            Approach and class room practice should be inter       connected

It is not so relevant whether they are bilungual or not, I guess, any student meets the same problems while learning - new Grammar, new sounds, new Lexics, new Syntax, new everything

If fully bi-lingual then there are no problems and in fact the knowledge of how different languages function can be practical and empathetic assets while teaching. If however at a learning stage of the language to be taught, perhaps some care can be taken as to choosing  the levels and skill bases to be taught. If such care isn't taken there is a tendency for teachers to fossilise and reinforce language mistakes. There are some gpod courses around which can improve teaching for both firt-language and non first language teachers and CELTA is one of these.

I dont think bulingual students will face much problem as some students excell in many languages. What is important is to make them used to the language more to familiar with its words and usages to master over it.