> Og svo var dátt með þeim öllum saman

According to CV, 'dátt' here is the neuter nominative singular of the
related adjective 'dár' (for the double 'tt', compare 'nýr' : 'nýtt').
See section Beta on p. 98: "in phrases expressing a charm of
fascination excercised over another, always of uncertain and fugitive
nature." This example is translated there as "they so charmed one
another that..."

http://lexicon.ff.cuni.cz/png/oi_cleasbyvigfusson/b0097.png
http://lexicon.ff.cuni.cz/png/oi_cleasbyvigfusson/b0098.png

(For the adjective, see the bottom of p. 97 and the top of p. 98. For
the related noun and verb 'dá', see further up the right hand column
of p. 97.)

Other alternatives with that connotation of a trance state: "they were
in such raptures over each other" or "so entranced/enchanted with one
another".