Eptir þat ríða þeir alla ina sömu leið

"After that they ride the whole (of the) same route".

'alla' must be f.acc.sg. here, agreeing with 'ina sömu leið'. For a
small number of parallels, I typed 'alla hina sömu' into Google.
Granted, Gwyn Jones does have "they all followed the same route";
maybe he was working from a text that had 'allir', m.nom.pl.



látum lausa hesta vára

"Let's set our horses loose [here]"
"We'll let our horses loose [here]"

'lausa' m.acc.pl. of the adjective 'lauss', agreeing with 'hesta'.
I suppose 'láta lausan' and 'leysa e-n' both mean to let loose, or
release, or set free, but I don't know whether they could be used in
all the same contexts. I wonder if there would be any difference
between:

leysum hesta vára
sleppum hestum várum

And would a Norse Mr Burns say: "slepptu hundunum"?