Your switches are single pole double throw with center off. You have a hot black pigtailed to the two switched with the red wire nut in the front of your switch box. The light switch has a yellow wire and a brown wire out of it, spliced together and connected to a black wire in one of the NM cables. The switch was probably meant for a light/nightlight combination unit and the old unit only had a light, as your new one does. The switch will operate the light in both positions with center off
Where your black hot enters the switch box, you'll have a white neutral that should be connected to a white wire from one of the cables going to the ceiling. That should put a black switched hot and a neutral up at the ceiling, possibly the one marked "l."
The other switch has a blue wire and a red wire that would be switched hots to turn on the vent or the heat depending on the position on the switch. The blue wire is connected to a black wire going up to the ceiling and the red wire appears to be connected to the other white wire going up to the ceiling, possibly the other cable.
Which ever white wire at the ceiling is the neutral, you'll connect it to the three white wires out of your new unit with a wire nut. The other white wire that appears to be a switched hot will go to the red wire out of your unit. That white wire should have some black tape wrapped around it to show it's hot. One of the black wire out of the ceiling, possibly the one marked "l." will go to the blue wire out of your unit for the light. The other black will go to the black wire from your unit for the vent.
You will need to verify which wire is which, we can't do that from here. You also need to verify the breaker will handle the load of the heater. The copper wires, ground wires, need to be connected together in the box and to the box. They also need to be connected at the ceiling and to the green wire out of your unit. The two cables going into your unit need the proper connector to secure them to the unit. The two cables are not code compliant and one of the NM cables would need to be replaced with a three wire plus ground to meet code.