Im not sure Maria I and Pedro III count as co-rulers
What is somewhat confusing to someone used to the Northern European way of doing things is that Kings Consort (unlike Queens Consort), at least in Portugal, were assigned regnal numbers. I cannot say whether Pedro III would count as a King Consort or a co-reigning King. He was himself the son of a King, and was next in line after his niece and wife, Maria I, his own children and his wife's sisters. Since he predeceased his wife, we do not know whether he would still have been regarded as King after her death.
He was after all assigned a regnal number, and the next Pedro on the throne, Pedro III's grandson, took the number IV. However, as the other example of a Portuguese King Consort tells us, having a regnal number does not necessarily mean that he counts as a reigning King. The second husband of Maria II, Ferdinand of Saxe-Coburg and Gotha, was given the style of King at the birth of their eldest son in 1837, and he is counted as Fernando II. Yet, despite having a regnal number, his status as King Consort rather than a co-reigning King is shown by the fact that his "tenure" as King ended on the death of his wife and the accession of his eldest son.
In Medieval times Kings sometimes crowned their favourite heir as junior king to make clear who would succeed.
Can anybody provide a list of these, throughout European royal history? Off the top of my head, I can name the following --
Queen Isabel I of Castel and King Fernando V of Aragon
Czar Ivan V and Czar Peter I ("The Great") of Russia
Queen Maria I and King Pedro III of Portugal
King William III (House of Orange) and Queen Maria II (House of Stuart) of Great Britain