First of all, you could consider measuring the existing group bond. This can be done using Zastrow's idea. According to Zastrow (1985) group bond or cohesion is ‘‘the sum of all the variable influencing members to stay in a group. . . . It occurs when the positive attraction of a group outweighs any negative implications a member might encounter’’
You need to list out the benefits for the members to stay together and then list out the costs of doing the same.
You then add the total scores for each and compare the average scores. If the average score for benefits is higher than the average score for costs, then the group bond is strong. If it is weak, you need to note the particular cost factor which the respondents have rated highly and work on that to improve the group cohesion.
Only a suggestion. Make all you can to foster the sense of belonging of each member of the group. The work by the social psychologist Henri Tajfel is here a must.