The red roses are 'Dr. Huey' rootstock. The pink rose was budded onto it, and the rootstock is taking over.
'Dr. Huey' is a rampant climber, which blooms once in the spring, and thereafter grows and blackspots. It needs to be removed from the roots, whence it springs.
If it's been this way for a few years, you would probably be best off to just dig the thing up and buy a new rose.
If you want a pink rose, there are many good ones.
If you want clusters of small red roses, there are, likewise, many lovely red single roses.
