9 days is whistle stop for a ring road tour, and here you are trying to do it without moving on every day, and having (potentially) long interior detours on unpaved roads. People have done it, but as a driving driving driving type of holiday, depends what you want.
Maelifell, Landmannalaugar
If you are hiring, you need a 4wd to go to Landmannalaugar. Check with your hirer to be certain, but most 4wds will do for this, and don't drive into a ford unless you are certain you can cross it, just because you are allowed to drive that road doesn't mean the ford is passable today, they can be unusually deep from time to time because of weather, which may be weather somewhere else.
Maelifell is by a road (F210) that many hirers will not permit you to drive a hire car, even a 4wd, unless perhaps it is a more robust grade of 4wd. There are some hirers that are not so specific about where you can drive, though obviously it is your problem and expense if you get stuck or damage the vehicle due to lack of care in driving, so you might think twice about going there unless you have hired a more robust higher clearance kind, and h ad suitable driving experience.
Lake Viti
There are 2 Vitis. The one at Krafla, 15km from Myvatn, no problem to go there. The other person has commented on the assumption you mean Viti at Askja. If you are hiring, you need a (proper) 4wd to go to Askja (because there are some serious fords). Also, they usually don't let you drive in from the E, because taht's a terrible road after the paving runs out, you have to drive in along one of 2 roads that come in from the north, one near Grimstadir and the other one is the next road further E. It's 4 hours each way from the ring road to Askja, 'cos its a bad road, much worse than Landmannalaugar approaches, so you go quite slowly.
can you get to this lake without a four wheel drive?
The one at Krafla, in a 2wd, yes no problem. If you mean the one at Askja, tes, you can also do it a coach tour out of Myvatn (or Akureyri for extra time in the bus). It's a long day tour so you need to stay overnight where you leave from.
Jokulsarlon to Akureyri is practically half way around the ring road, just to let you know the magnitude of what you propose. The ring road is 1350km around, excluding getting to the airport and back.