I seem to have plenty of blossom drop on beefsteaks, but they set fruit eventually. Patience is all I can suggest, but someone else might have another suggestion.

How old is the plant? Unlike your other two varieties, Brandywine is a late season variety at 80-85 days so early season blossom drop is common while it is focused on growth and root development. Several previous discussions here about this and how one cannot accurately compare different varieties. Linked one of them below.

Dave

Here is a link that might be useful: Brandywine no fruits - why? discussion

we usually see bw holding blossoms around the same time as the other 2 are setting fruit. A little long this year, but I guess patience is my only choice right now.