Different opinion
From a linguistic point of view I have a very different opinion about the family of romance languages. French, Italian Spanish and Portuguese having all derived from Latin have similarities BUT many differences. The similarities are most apparent in the grammar patterns i.e. syntax and rules but phonetically and intonation wise these languages are quite unique. The vocabulary is sometimes similar but the gender may differ from one language to another because the origin of words in each language that is not Latin differs from language to language. The borrowed words in Spanish are either Greek or from the Moors. Words like ojalá, azúcar, almohada, alcázar etc. are examples. The Greek words are easy to identify because they end with [a] but are masculine in gender. For example el problema, el sistema, el programa and like words.
Italian is still the closest to Latin vocabulary and grammar wise. French is the most different in comparison to the other three because it had more time to evolve (away from Latin). French is phonetically unique when comparing it to an extremely phonetic language like Spanish. As well, French grammar in certain aspects differs very much from Spanish and is very difficult to master whereas Spanish grammar can be mastered at a high level if one has the proper educational training. Even French speakers admit how difficult French grammar is.
I just wanted to add my opinion since I can see how these languages are similar but yet VERY different therefore I am very careful when making comparisons. As well, Brazilian Portuguese is very different from Portuguese from the homeland. In my opinion Portuguese from Brazil is easier to understand but from Portugal the phonetic aspect is really a challenge.
The similarities in grammar are for example:
1) ser/estar= Spanish, Italian, Portuguese
2) concordance (nouns and adjectives)= Spanish, Italian, Portuguese, French
3) usage of the subjunctive (in order of importance IMO)= Spanish, French & Italian (a tie). I can't comment regarding Portuguese.
4) Reflexive verbs (verbs that are reflexive in these languages are not in English in some cases)= Spanish, French (I can't comment on Italian & Portuguese)
5) L'accord du participe passé (one aspect of this rule)= French only (and not easy for everyone).
6) Verbs= certain verb tenses are more commonly used than others= Spanish stands out here compared to French and Italian.
There are more comparisons but I will stop here.
Je m'en vais.
Salut,
LDG.