Rabbit have an incredibly high risk of going into shock or getting hypothermia if given a bath
The rabbit might be "ok" or he might die it's just really not a risk worth taking
For flea treatment you have to be very careful as medication made for cats and dogs can be extremely toxic for rabbits
I would recommend getting a flea comb and spraying the enclosure with apple cider vinegar
The baby looks to be around 5 weeks old
Make sure to separate ASAP if the rabbits are left together they WILL have more babies
Lennon the bunny on YouTube has some videos about catching feral rabbits
You could also try contacting your local rabbit rescue for advice and maybe with traping...