My question is: which one is correct to talk about two figures in my writing?
"Figure A and B are ..."
"Figures A and B are ..."
Number two is correct. The predicate is "are," which is the predicate for a plural subject. The subject is "figures," which is plural. A and B modify the subject but don't affect its plurality.
"A" And "B" are names of your figures, and so the phrase "A and B" is a compound appositive. See e.g. http://www.qcsd.org/cms/lib04/PA01000005/Centricity/Domain/229/appositives.doc
There are two different figures, so it seems logical to say "Figures A and B..."
It would be correct to say "Figures A and B are...". An alternative would be to say "Figure A and Figure B are..."