Being the son of an Infante, Pedro Carlos was not Infante of Spain by birth, but by grace. Children of Infante Gabriel were created Infantes of Spain by their grandfather Carlos III
No husband of a Portuguese princess was ever created Infante or settled in Portugal after the wedding in the same situation of the above mentioned.
Only two foreign princes were ever created Infantes of Portugal.
The first was the spanish Infante D.Pedro Carlos de Borbon y Braganza.
He was the son of Infante Gabriel of Borbon, the brightest of Carlos III's sons and allegedely his favourite, and Infanta D. Mariana Victória de Bragança.
Both Gabriel and Mariana died suddenly from smallpox in 1788 when Pedro Carlos was only 2 years old.
In 1788, Queen D.Maria I, had also lost, her elder son, Prince D.José who died w/o issue.
Her second son, D.João (VI), had married the infamous Carlota Joaquina of Spain, Gabriel's niece, but, in 1788, the marriage had not been consumated as Carlota Joaquina was only 13 years old.
So, by 1788, Pedro Carlos was the Queen's only grandson, reason why the Queen asked for him to be send to Portugal and raised as a Portuguese prince and eventual successor.
Carlos IV of Spain accepted and the Prince was dispatched to Portugal where he was created Infante of Portugal - he was by birth Infante of Spain.
Pedro Carlos grew up in the Portuguese court, accompanied the RF to Brazil in 1808, and married his cousin Infanta D.Maria Teresa de Bragança, elder daughter of D.João VI and D.Carlota Joaquina in Rio de Janeiro in 1810.
The wedding did not last long (1810-12) as Pedro Carlos died suddenly, leaving a son, D.Sebastião de Borbon y Braganza, the second and last Infante of Portugal and Spain.
Let me get this clarified: I believe that the husband of a Spanish princess was created into an Infante of Spain by GRACE if he met the following conditions --
1) He himself was a born prince
2) He settled permanently in his wife's native land
As it was, both daughters of King Alfonso XII married men who qualified (Prince Carlo of Bourbon-Two Sicilies and Prince Ferdinand of Bavaria). Accordingly, both were granted the title Infante of Spain (but not the style of Royal Highness, since they already had that). Both Infantas (Maria de las Mercedes and Maria Teresa) retained their succession rights and transmitted them to their children.
Is this correct? What about PORTUGAL? Did the same rules apply there? Was there such a thing as a Portuguese Infante by Grace?