Hi All,
I'm looking for something to go with a picture to go with marriage vows.
I have two knots tied to each other and one side will say "Tethered to you", so I'd like to get that translated.

The other side is still undecided, so I'd like to get a few things if possible:
"For Better or Worse"
"Through Good or Bad"
"Through Storm or Calm"
"No Matter What or Come What May"
Other ideas on that one welcome!

"Tethered to you" --> Nasctha leatsa
Tethered together --> Nasctha le chéile

"Through Good or Bad" --> Trí mhaith nó olc

I would be a fan of repeating the "trí" here. English is a bit more lenient in this respect than I think.

Trí mhaith nó trí olc I am open to correction however.

I thought "ceangailte" upon reading the OP (ceangailte le chéile), but I suppose nasctha works too.

What is the difference between dona and olc?

Dona is an adjective an duine dona - the bad person.
Olc can be used as an adjective but it would normally be used predicatively Tá an duine olc - the person is bad/evil

In the phrase you asked for olc is a noun meaning bad(ness)/evil, it might be clearer if you use the article..

Tríd an mhaith nó tríd an olc - through the good or through the bad.

Hope that helps a bit.