My first answer was somewhat rushed and therefore not accurate to this specific context so this is now my corrected answer after time for some further research:

As you say, it's referring to a group life insurance policy (sometimes also called death in service) and the "double effet familial" to a provision in this policy - this is where the systems differ across countries it seems because employers would need another specific policy for "spouse and partner group life assurance" in the UK in order to provide this same lump sump benefit for the death of the spouse or partner as well. E.g. Aviva's product information guide (https://www.aviva.co.uk/adviser/documents/view/gr01162.pdf) refers to being able to "combine Group Life cover with our other policies, such as Group Critical Illness, Group Income Protection and Group Spouse/Partner Life cover".

Unum defines these spouse/partners policies as: "A policy is taken out by the employer to provide a lump sum benefit to an employee should their spouse or partner die while insured" (https://www.unum.co.uk/group-life-insurance). This is therefore an additional policy to the main policy that covers the employee, which of course is somewhat different to the French context in which this all falls under one policy.

I fear anything too literal would likely not be understood so the translation I would suggest would be something like "group life insurance spouse and partners benefits" (or something similar) to convey the benefit of a lump sum payment associated with spouse/partner group life insurance/assurance policies.

Hope this helps!