Is there any proof that Mark or Luke walked with Yahushua? I tend to stick to Yahushua's words and those of the Apostles.Nothing seems to be lost when we omit Paul,Luke and Mark..(I am not saying their words were not good.) Pamela 
Zero, zilch, zip... nada.

If they Agree with The Law and the Testimony of the Prophets there is Light!

They (with Historic record) are only valid for collaborating evidence.. I think thats the term...
they will not stand on their own or even together as two witnesses.

One of them or both of them with an eyewitness (IaHUChaNaN)
Still do not equal to two witnesses as to specifics,
but Will substantiate the basic Facts of the case.
They tell us that He Lived, was rejected, betrayed, executed, entombed..
and that He was Resurrected (and Ascended) according to Promise.
Same with MaTiTIaHU as far as the narration goes..
The Sayings However Were from an eyewitness account
so together with IaHUChaNaN make Two Witnesses.
Copies and Translations are another problem.
But We Do Have a Second Witness to IaHUShUA's Word
IN that SetApart Spirit of IaHUeH who brings to our mind everything that He Spoke and Taught..
and even further to All Truth.. but in this case it is a bit at a time... as we learn and digest
and do so accordingly... we are given more to chew on.. Ohhhh how Wonderful!!!!!
Sometimes this SetApart Spirit of IaHUeH will disagree with the wording of The Words.
In this case No two witnesses... but by this point we Know that we Can TRUST IaHUShUA
to Help us to Sort it All out!.