Looks like this was a tough one fro everyone. No matter I think i figured it out after reading the following guidance:
What I think this means is that whilst he is stateless (technically) if he applies at the same time as me (the main applicant) then he is taken to be my family member and nationality is not an issue.
I'm going to make the application and see what happens.
https://assets.publishing.service.gov.u ... __EXT_.pdf
3.5 Dependants included in the application
Spouses or partners and dependent children already accepted as such who are
accompanying the applicant in the UK should, irrespective of their national status, be
included in the application form. Where no previous application has been made for
leave to remain, spouses or partners and dependent children can apply as the family
members of a stateless person providing they meet the relevant requirements of the
rules for dependants.
If a spouse or partner or child wishes to be considered individually as a stateless
person, they must complete and submit a separate application. Where the factual
basis for family members is the same, any related applications must be linked and
considered together. If the main application is granted, family members are granted
leave in line with the stateless person.
Note: Will update after application, for anyone that faces the same situation.
