Yes, this is allowed for EU passport holders depending on how long you spend outside of Brazil in between visits, and how long your visits last.
Exception: this regulation does not apply to citizens of Croatia, Portugal, Poland, United Kingdom and Ireland.
As seen on their website Brazil allows:
The 90-day period begins on the date of first entry and ...
Free movement also covers short-term travel, so your being in France is sufficient for this trip to constitute "joining" you. But unless your family relationship falls under the free movement directive, your relative will need a standard Schengen visa with the application requiring the larger set of supporting documents.
If you don't live together, it is ...
According to https://www.gov.uk/guidance/visiting-the-uk-after-brexit
What you'll need to do to visit the UK after the UK leaves the EU, including whether you'll need to apply for a visa.
If the UK leaves the EU with a deal
If the UK leaves the EU with a deal, what you’ll need to enter the UK will not change until 2021.
If the UK leaves the ...