I am very sorry to hear about the loss of your Brazileros.
The red and yellow Brazileros are the same species just different color morphs. They can certianly pair off and and breed. Most seahorses if given the opportunity will choose a seahorse of the same species over another species, so you should be fine introducing a single male.
I like to do a water change or 2 after a loss as well as waiting a few weeks before any new additions are introduced.