How to get my B team promoted to playable league?

I'm in my 7th season and finally thinking about using my b team as first team experience for my players. I'm in la liga, and my b team is in non playable league. will adding good players in my b team help me get promoted to a playable league?

also when my players are in b team, i know they use the same training facilities as my a team. but will they also use the coaches as well?

It's mostly reputation based I believe but you are relying a lot on luck

It depends on which non-playable league they are in. If they are in the unplayable league directly below your lowest loaded league, then they will come up eventually, though it is weighted on reputation, so the higher their rep the more likely they are to appear. If they are 2 divisions below your lowest playable league (assuming you have already loaded Segunda B), then you will never see them in game. I have the same issue with RB Leipzig in Germany. Loaded down to 3.Liga, but my II team are in the 6th division, so there is no chance of them ever getting promoted to a usable level.

my to increase the rep of my b team?> its reputation is obscure.

I have never seen a B team get promoted from below the lowest playable league. Not only that, when working on a Faroese structure (which has B teams present, as in Spain), the six B teams in the bottom division simply never get promoted if the league is inactive, despite their respective first teams being several divisions up and not presenting any possibility of a clash. Activate the league, and lo, B teams start getting promoted

Now, it's certainly possible that this is a limitation that only applies, for some reason, to created league structures. But I wouldn't go holding my breath.

With managing Murcia and them in the Adalante, the B team are in the lower division below the Segunda B. After a couple of years of improving the club, getting promoted and up to the top of the BBBA then, improving the facilities etc, throwing the players promoted from the youth team as they were too old but not good enough for the first team into the B team will always end up getting the B side promoted to the playable Segunda B then. Though the B team are not in a playable division the players do get simulated appearances etc so if you've Segunda B standard players or that in there the side will eventually get simulated promotion to the playable division then. My B team are in the B playoffs this season and will in all likelihood get promoted to the Adalante, which has usually happened for me in previous versions of FM. The B teams just can't play in or above the division the senior team is in.

With managing Murcia and them in the Adalante, the B team are in the lower division below the Segunda B. After a couple of years of improving the club, getting promoted and up to the top of the BBBA then, improving the facilities etc, throwing the players promoted from the youth team as they were too old but not good enough for the first team into the B team will always end up getting the B side promoted to the playable Segunda B then. Though the B team are not in a playable division the players do get simulated appearances etc so if you've Segunda B standard players or that in there the side will eventually get simulated promotion to the playable division then. My B team are in the B playoffs this season and will in all likelihood get promoted to the Adalante, which has usually happened for me in previous versions of FM. The B teams just can't play in or above the division the senior team is in.

While players in B teams may get random appearance stats, the quality of players in your B team makes no difference to whether they get promoted or not (the actual league is not simulated).

As others have said, it is weighted chance based on reputation, which is hardcoded at the beginning of the game.