CRM IN FILEMAKER CALL CENTER

I am developing my own CRM in Filemaker to use it on the web. I need some experienced part-time developers to help me, to complete and correct some script for this crm. 1) Main problem is : I want only one user at the time thet can go on a record. Sound easy, I know, but so far (using my script), sometimes still happen that 2 users go on the same record contemporary. 2) I integrated a sort of "click to call", using x-lite and command sip from browser. Everything is fine expect that I cannot hang up from browser. I need to do this. 3) Eventually I need an integration of this filemaker crm with the predictive dialer of [login to view URL] this last part resident in Ukraine are prefferred.