Hello friends I have doubt with fixing balsa sheets . Which glue is best for fixing balsa

Cyano is the best. The thicker variety is better, as it gives you a little more time. And, you must understand the adhesive bonding methodology. Thin cyano has a strong "wicking" action, ie capillary action, and often it is better to hold the parts together and let the cyano enter the gap through this action. Lastly, remember - with cyano and balsa try to get it right first time. If you have to glue on a surface earlier treated  cyano, you will not get the same bond strength