Cóisire - - a wedding party
I would probably write bhí grúpa amuigh ag bainis
but Tomás omits the verb. Bhí is understood
and cóisire is a better word than grúpa bainise
Which just goes to show how much I have to learn!

There was a group "out" - - amuigh i.e. away from the island on the mainland;
arbh olc an scéal (dóibh) -- for whom it was a bad plight or situation.
This is the verb is, - - the copula - - again in the past tense (ba) before a vowel,
this time combined with a relative pronoun (ar).

An forainm coibhneasta - - The relative pronoun,
is one of the more difficult constructions but is easily learnt.
I will come back to it again but for the moment I refer
students to New Irish Grammar, Fallons, Chapter 31, page 143