I don’t think the problem is coming from the ArduinoOTA.
I just removed the includes and code refering to OTA, webserver, DNS and httpupdates :
//#include <ESP8266mDNS.h>
//#include <WiFiUdp.h>
//#include <ArduinoOTA.h>
//#include <ESP8266WebServer.h>
//#include <ESP8266mDNS.h>
//#include <ESP8266HTTPUpdateServer.h>
But still the same error on the SimpleTimer:
error: redefinition of ‘class BlynkTimer’
#define SimpleTimer BlynkTimer