co-grandnephew-in-law

Spouse's grandnibling's husband.

co-grandnephew-in-law.

great-grandnephew-by-marriage-in-law

Spouse's great-grandnibling's husband.

My great-grandnephew-by-marriage-in-law is a good person.

step-great-grandnephew

1- Sibling's step-great-grandson.
2- Stepsibling's great-grandson.

My step-great-grandnephew is a good person.