Does it count as davening with a minyan to daven mincha with a minyan davening maariv (and maybe the opposite also)? (if you could give sources would be appriciated)
My understanding of your question is as follows: If for example one person has to daven his silent Shmoneh Esreh for Mincha when he's a bit late and he walks in to an early minyan of Maariv where Shmoneh Esrah is being said, is this considered that he is davening with a minyan? The question being can he who is davening Mincha be considered part of minyan of those who davening Maariv? If this is indeed the question then you have touched upon an issue in this issue that is in dispute among the Achronim. (If not please write again) According to the Mishna Brura, the very fact that he is present in the Bet Knesset davening where there is a minyan it is considered that he is davening with a minyan. The Mishna Brura actually discusses the case of one davening Shacharit while the Tzibur is davening mussaf, that it is considered that he is davening with a minyan, however the same principle would apply in the case of Mincha and Maariv. (,ע"פ צל"ח ברכות דף ו ע"א'ס"ק ל ו סי' רל"ו ס"ק יא משנה ברורה סי' צ' ). However, the Magen Avraham and the Taz (סי' רל"ו) as well the Chayya Adam (כלל לד:א) disagree and they see it as contradictory since one is in the Tefilla of day and one is in the night Tefilla. Nonetheless, in the Sefer "Hatefilla b'tzibur", the author, Rav David Fuchs shlit"a follows the opinion of the Mishna Brura, that it is considered tefilla with a minyan.