Michelle tells Jenny she's on her way to work
Michelle - Ar fy ffordd i'r gwaith ydw i nawr

Note that she says i'r gwaith - 'to the work', not 'to work' as in English. You must also include the word 'the', when you talk about going to school - i'r ysgol, to town - i'r dre, to church - i'r eglwys, and to hospital - i'r ysbyty.

It's Michelle who found out about Jac's new garage, as she points out to Brian:
Michelle - Fi wnaeth ffeindio mas fod Jac yn mynd i brynu'r garej ontefe?

If Michelle were making a simple statement about what had happened she'd have said:

Gwnes i ffeindio mas fod Jac yn mynd i brynu'r garej'
'I found out Jac was going to buy the garage.'

But because she's emphasising the fact that she was the one who'd found out about the garage, she starts with 'Fi' followed by the verb 'wnaeth'.
'Fi wnaeth ffeindo mas' - 'It was I who found out.'

You can use this emphatic pattern with other verbs as well:
Gwelais i means 'I saw', but if you want to say 'It was I who saw', you'd say 'Fi welodd'.

Atebais i means 'I answered'. But, for emphasis, you'd say 'Fi atebodd' - 'It was I who answered.'

When Jenny rushes in and announces a crisis, Agnes asks 'Pwy greisis?'
In formal Welsh you'd say 'pa greisis', but in speech it's perfectly acceptable to say 'pwy greisis'.
Let me refresh your memory about the question words pwy, beth and pa. 'Pwy' means 'who' and 'beth' means 'what'.
'Pa' also means 'what' but 'pa' must be followed immediately by a noun, as here: 'pa greisis?' - 'what crisis?'