there is 同 that is 有咩分別

Hi, {that is} and {there is} are the same meanings, no difference.
In ur sentence {there is Tom and Peter}, {there} should be relatived to something/case which is mentioned before this sentence; also {is} belongs to {there}, not relative to Tom and Peter. that is why here using {there is}, not {there are}.
e.g. They are Tom and Peter. (are) belongs to (they)
e.g. Tom and Peter are here. (are) belongs to (Tom and Peter)

'THAT IS' AND 'THERE IS' IS TOTALLY DIFFERENT.

THAT IS MARY----果個係 MARY
THERE IS TOM AND PETER,果邊有阿TOM 同阿 PETER。

THOSE IS NOT THE PLURAL(眾數) OF THERE,IT'S THE PLURAL OF THAT,THE PLURAL OF THIS IS THESE, THERE HAS NO PLURAL.

你又問 點解唔係"Those are
之後又 點解係用"There is"唔係用"There are"既

究竟你想講 點解唔係用 those are 定 there are 呀?