Edit January 19: FLI has made a substantive statement about this issue:
https://futureoflife.org/rejection_statement/
This seems concerning. It is claimed that the Future of Life Institute, run by MIT professor Max Tegmark, offered but did not pay out a grant to a Swedish far-right foundation. The character of this foundation and its associates is well-known in Sweden. Expo is an old and respected watchdog organization specialized on neo-nazism and related movements.
https://expo.se/2023/01/elon-musk-funded-nonprofit-run-mit-professor-offered-finance-swedish-pro-nazi-group
Brother is used as a term of affection in a fair few languages (including Swedish), so I wouldn't just trust a tweet.
The Swedish wikipedia article on Per, however, confirms more definitively that they are brothers: https://sv.wikipedia.org/wiki/Per_Shapiro