personally i would have a male fighter and 4-6 females in the larger tank and maybe a small number of corys or skunk loaches. and leave the dannios in the 25l.
others will disagree with putting male and female fighters in the same tank as the male can harass the female too much but if theres 4-6 then the pressure from the male advances will be spread out amongst the girls.
but there are some rules to doing this.
get all female fighters from the same person, shop, tank. as if they have been seperated they can be agressive towards each other.
have a long finned fighter as having longer fins makes him slower so the girls can run away faster.
and plant it, so that there is a bit of cover for everyone so that line of sight can be broken between the fish.
and have low water current
when i first started fish keeping this is how i had my first setup and was great as you always get to see the male flaring to the girls