Update: E.G.Palmer asks in a comment, whether illustrator Frances Brundage is related to illustrator Margaret Brundage of Weird Tales fame. That was a question I was going to address first time around on this post, and then promptly forgot to.
SO, the short answer is 'no', from what I can tell. Frances Brundage was born Frances Lockwood, daughter of Rembrandt Lockwood, an artist himself. Frances married William Tyson Brundage, also an artist, and they had a daughter who died as a baby. So it is possible that Margaret is related in some in-law sort of way, through her husband, but I haven't determined that yet.
A personal side-note of interest (to me) is that I find I'M distantly related to Frances, through the New Jersey Lockwoods. Rembrandt Lockwood is in my family tree, zig-zagging back aways. Though I can't say I'm particularly proud of that, when I read that Rembrandt Lockwood abandoned his family, forcing Frances to seek livelihood at the age of 17.