One reason the 12 apostles would not consider modern Christianity as valid is that some biblical words do not have the same meaning today as they did in their original form.
The word ‘cross’ is an example. Originally it meant a single pole, with no additional cross bar, on which criminals were nailed. The two beamed cross that we see outside churches today had its origin in the worship of the God Tammuz. In the middle of the third century the two beamed cross was used by the early churches to attract pagan converts.
‘Baptism’ comes from the Greek word ‘baptizo’ meaning to dip, as in the dyeing of cloth which required full immersion. It never involved pouring or sprinkling.
‘Hell’ had several meanings depending on what Greek or Hebrew word was used. The only Hebrew word for Hell in the Bible is ‘Sheol’ which is translated grave as often as it is used for hell. It means the place where everyone goes at death. Turning to the Greek word ‘Hades’, this has the same meaning as ‘Sheol’ in Hebrew. We also have the Greek word ‘Gehenna’ which is often translated Hell, and means the garbage dump of Jerusalem where fires always burned the rubbish and maggots thrived. Gehenna means the disgraceful end of those condemned at the judgement day.
‘Nephesh’ in Hebrew and its associated Greek ‘Psuche’ (translated as soul) both mean breathing creature and can refer to animals as well as people.
The Hebrew ‘ruach’ and its counterpart in Greek ‘pneuma’ which are translated ‘spirit’ means wind, breath or mind.
To ensure you get the true meaning of biblical terms look up the original definitions in Hebrew of Greek. These can be found in Vines commentary or Strongs/Youngs concordances each of which provide details of the original meanings. Many on-line Bibles also provide a quick and easy option to find the original meanings which enable you to compare original with todays meanings.