Yes, booking classes are a fuzzy thing with LATAM nowadays.

Please take this with a pinch of salt, but Q should be one of the more entry level booking classes. It definitely does not allow for upgrade via coupons or miles, but as a long haul, should (still) include at least one piece of luggage of 23 kg (this can of course change depending on your origin and potential OW status).

B for the domestic leg sounds like a more premium booking class, at least from the plus basket, and should entitle you to one bag as well.

If these are booked as one ticket, the international allowance should be the one that also rules the domestic bit.

However, 100% reliable information can be obtained through your local LATAM customer service.