Breakdown of Ellos comen demasiado y solamente hay tres pasteles.
y
and
comer
to eat
ellos
they
haber
to be (there is / there are)
Questions & Answers about Ellos comen demasiado y solamente hay tres pasteles.
Why is it demasiado and not demasiados if Ellos is plural?
In this sentence, demasiado is an adverb describing the verb comen (how much they eat), meaning "too much". When used as an adverb to describe an action, it never changes its ending. If it were describing a plural noun instead, like "too many cakes", it would act as an adjective and change to match the noun: demasiados pasteles.
Could I use solo instead of solamente here?
I know hay means "there is" or "there are", but why doesn't it change for the plural "three cakes"?
The word hay is a special form of the verb haber. In Spanish, we use exactly the same word whether we are talking about one thing ("there is") or multiple things ("there are"). It never takes a plural form like regular verbs.