Relay and Apollo Client both can be used?

I'm developing a front-end with Next.js where GraphQL will be processed from GraphQL API endpoint. Hasura is being used as Back-end.

One of my colleague told me that some developers use Relay along with Apollo Client. I told him that why we should use both? If Relay is used then stick exclusively to Relay (no need to use Apollo also).

My questions are:

1. Can really both be used in a single project?
2. If i go with only Apollo Client what will be the consequences? (i have gone through documentation of Relay but found it really complex to integrate with Next.js).
3. Is there really need of Redux along with Apollo Client? (It's a market place website, lot of data with pages).