My garage is supplied from an old system 30A fuse in house by 2.5mm armoured cable to a garage 2 way fuse box - 6A light and 16a ring circuit
The ring circuit serves washing machine, tumble dryer and freezer - plus (occasionally) a 1.5kw heater
I would like to replace this garage unit with RCB protection and at same timeplan to wire in my garden shed where I would plan to have lighting, and a couple of sockets for hand tools (possibly with the 1.5kw heater from garage)
I cannot get access back to the house consumer unit to lay a second supply but what I thought to do was replace the garage fuse box with a 2 x rcd, 2 x mcd (1 x rcd and 6A and 16A mcb for garage supply and 1 rcd for shed - and run 2.5 mm armoured to shed (Shed already has consumer unit with 1 rcd, 2 x mcb) - However all the garage consumer units only seem to have 1 rcd

I have been given 3 differing pieces of advice from 'experts'
1 - Take a fused spur off the garage ring circuit and run to shed consumer unit
2 - Split supply from house at a junction box in garage and use 1 to feed a new garage rcd/mcb consumer unit the second feed to shed consumer unit
3 - Fit a (house) consumer unit in garage with 2 rcd (1 garage 1 shed) and 2 mcb (garage) - I am uncomfortable with this one - Why make a specifis garage unit if that is not what you are supposed to use

It would be appreciated if anyone could offer some unbiased advice

I don't understand the terms rcd/mcb/RCB and ring circuit.
Master circuit breaker? Remote circuit breaker?

#1 Seems OK. You can still put a 30 A circuit breaker to feed the shed.

#2. I would modify by using a dual lug ( see dual rated two-barrel Mechanical Solderless Lugs Tap Connectors Grounding Clamps Split Bolts Street Light Kits ) in the garage panel. No need for another junction box. You can't have two wires in the same lug. You can also pigtail in the panel.

KISS poster is non-USA.