There are no financial or accommodation requirements for family reunion applications to join immediate family members who are refugees in the UK. You can find guidance on Family Reunion for refugees on GOV.UK.https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/541818/Family_reunion_guidance_v2.pdf
Extended family members can also sponsor refugee children to join them in the UK under the Immigration Rules. Those applying must show that they can provide adequate maintenance and accommodation that is suitable for the child’s care. This is set out in the Immigration Directorate Instructions on GOV.UK:
Where an application fails under the Immigration Rules, including where an applicant is unable to meet financial or accommodation thresholds, our policy requires caseworker to consider whether there are any exceptional circumstances for granting a visa outside the Rules.