We have 4 rose bushes in our garden. When we first planted them, one
had yellow roses, one had white, one peach and one pink. Now they are
all dark red, kind of like a dark magenta, and the flowers are shaped
in a strange way, they open out really wide and flat and they don't
have curved petals like they did when they were first planted. The
yellow ones aren't in the same place as the rest, but they also changed
colour and shape. BRBR

Your plants were originally grafted, undoubtedly to the most common understock
used in the USA, 'Dr. Huey'. At some point, the scion (the part above the
graft) has died out, and the new sprouts came from below the graft -- the 'Dr.
Huey' portion. 'Dr. Huey' is a deep red, semidouble variety, which blooms only
once a year in late spring or early summer.