Will Attestation and Execution

Dear Lawyer, Kindly throw some light on the following questions Genuineness of the will is in question due to variation in signature.The attesting witnesses are alive and ready to testify.The testator is dead. The scribe who prepared the will on basis of testators instruction is alive, but is not an attestor.He is plain eye witness 1. Is it mandatory that attesting witnesses has to fully read the contents of the will in entirety and understand before signing the document ? 2.How can the execution of the will be proved ? ( i.e the testator not only signed but has fully understood its contents. ).As testator is dead, nothing can be said from his mouth whether he understood . Who has the onus to prove that testator has read, understood the will before signing it ? Is it the scribe who prepared will or the attesting witness or someone else ? 3.If the beneficiary was merely physically present at time of attestation and execution of will, will it be considered as suspicious circumstance ?