For example:
Irish
"Tá siad ag súil go mór lena n-uncail a fheiceáil."

English:
"They are looking forward greatly to seeing their uncle"

I don't know how to phrase my question... but if somebody could explain what's happening grammatically here, and in situations like this (where the last word is a verb) I'd appreciate it...

Irish:
"Ba mhaith leo due go dtí an fharraige chun seoltóireacht a dhéanamh."

English:
"They want to go to the sea to go sailing"

Thanks

It's an infinitive construction. a n-uncail a fheiceáil = 'to see their uncle', literally 'their uncle to see(ing)'.

_________________
I'm an intermediate speaker of the Corca Dhuibhne dialect of Irish and also have knowledge on the old spelling
Soir gaċ síar, fé ḋeireaḋ thíar

I don't use that structure much but if it does you need to review your grammar
geometry dash lite