Read book from different Apple ID account

Presumably these are purchased eboooks?

Purchased content is tied and licensed to one Apple ID. It won't be usable on another Apple ID - but there is a solution.

You could set up a Family Sharing group with yourself and all content of 'members' in a sharing group will be able to share bought content. In that way your various devices signed in with different Apple IDs can share and access the same content.

See Set up Family Sharing and What is Family Sharing?

Set it up with the Apple ID with which you want to continue buying content. It is this account which will bear the cost of buying content for all the other members.

That's valuable information tamikay. It would seem that some data matching is preventing the mixing of your two Apple IDs in a family group. Possibly some major surgery on some data in your lesser-used account - a variation on a name for example - might resolve this roadblock.