I fed some of my old fish breadcrumbs but then swimbladder kicked in and killed them both was it the bread crumbs?

Possibly yes, especialy if you said it was swim bladder.
As I have read carbs are no good for goldfish.
The bread, especialy if dry can and will expand in their tummys and mess with their swimbladder's inflation.
Comercial fish food is something to stick with untill you read up on alternative foods for goldfish.
Someone here should be able to supply the link.

Never feed ur goldfish bread or rice. No no no.

Are these older fish or the shubunkins you have now?

Older fish. The shubunkins have only been f.ed fish food flakes