mtftp would be what you're looking for. HOWEVER, you are very quickly going to learn wireless (esp. old 802.11b hardware) and multicast do not play well together. Outside Uverse circles, it's hard to tell what wireless APs can deal with multicast -- Uverse has wireless receivers fed from an isolated AP, but the limit of 2 STBs suggests they don't work so well either.
At layer-1 and layer-2, Wi-Fi is used instead of a wired protocol like ethernet.
Above that, the layer-3 protocol (IPv4, IPv6, etc.) will be the same, as will the layer-4 protocol (TCP, UDP, etc.).
Protocols above layer-4 are explicitly off-topic here but they will be the same as used on a wired network.
The whole idea behind the network stack is that each layer in the stack is independent of the other layers in the stack. For instance, IPv4 happily runs on many different layer-2 protocols (ethernet, Wi-Fi, PPP, frame relay, HDLC, etc.), and it doesn't know or care which layer-2 protocol carries it. Layer-2 protocols, such as ethernet and Wi-Fi, can carry any number of layer-3 protocols (IPv4, IPX, IPv6 AppleTalk, etc.), and they don't care which layer-3 protocol they are carrying.
As far as an application is concerned, nothing has changed, because the application is oblivious to the lower-level protocols being used.
Best Answer
Lets test this out then. If we send multicast packets to multiple devices connected to a WiFi access point at a constant rate, then the access point should report the same amount of traffic.
To run this test, I'm sending packets from a wired PC to an an android tablet and a raspberry pi. Don't have any iOS devices. The network testing tool iperf can easily be used to send and receive these packets with the following settings:
Server (Devices on WiFI): iperf -s -u -B 230.5.5.82
Client (Wired PC): iperf -u -c 230.5.5.82 -t 60 -b 1M
With these settings we're sending multicast packets at 1Mbps for a minute. Running this test and looking at the wireless traffic on the access point shows it is consistently about 1Mbps so it must be doing true multicast. The other notable thing from the results is that the packet loss is really bad at well over 50%. This is likely because multicast packets are getting sent at the lowest possible speed so lets force the access point to only run in the fastest speed. I'm using a WRT54GL running dd-wrt where the setting is called "Transmission Fixed Rate". Running the same tests again after setting this to the fastest speed gives a much more acceptable packet loss of less than 5%.
To actually answer the questions:
Get the fastest access point that allows you to fix the transmission rate and that supports multicast. There are definitely access points that do automatically convert multicast packets to unicast. For the speed issue, it isn't enough to just use a wide 5GHz channel since there are a number of different speeds that clients can actually communicate at.
Can't imagine things would work differently on iOS devices since the main determining factor would be the access point.
See 1 as it depends on the access point.
Edit: After testing things out more and on some ac APs, it turns out the important thing for mulitcast is being able to set the available rates. Multicast still uses g speeds so the available physical rates are 6, 9, 12, 18, 24, 36, 48 and 54Mbps. Most APs are going to default to the slower speeds so being able to disable them to force it to use the higher rates will give a huge speed up. Being able to set this is probably the most important criterion for a multicast AP. As an example, in modern versions of DD-WRT, this can be set using the "wl rateset" command on the command line. It sure is well hidden and most firmware doesn't allow this to be set.