Did Jesus have fleshly brothers and sisters?
Yes, he did, for the words found at Matthew 12:46-50 make this very clear.
There we read that as he was indoors speaking, his mother (Mary) and his brothers (James, JoSeph, Simon, and Judas) had been standing outside waiting to talk to him. And at Acts 1:14, we once again read of Jesus’ mother and brothers being present (along with his Apostles) shortly after he ascended to heaven.
So, were these in fact Jesus’ fleshly brothers, or could the writers have been referring to ‘spiritual’ brothers?
The context in each case provides the answer.
Since Jesus’ brothers are mentioned as being there along with his Apostles, his disciples, and his mother (Mary) in the account in Acts;
These had to be his fleshly (half) brothers (other children of Mary).