Hi I am installing a 100 amp 24 slot subpanel in an unattached garage 50 ft away and plan on running 4 wires from the main 200 amp panel in the house, do I use a 100 amp double pole breaker in the feed panel from the house or do I use a double 50 amp breaker?

Thanks

That depends on the size wire your will be using. The breaker protects the wire not the panel.

A couple of other things:

1) Will the main panel accept a 100 amp breaker. You need to verify that.
2) Did you size the load you need to service. 100 amp can support an small home.

Thanks, yes I already put a 100 amp breaker in the main panel, and using 2/0 wire. It's actually like a small home 28 x 40 1 1/2 story with small kitchen a full bathroom and heated floors so there will be two hot water heaters and two garage door openers and of course receipts and lights

Depends on the wiring and load. Water heaters pull a lot of amps. Either way you get the same protection since the 50's are bridged. Just use the best quality breakers and a good ground source.

Assuming 2/O UF aluminum cable a double 115 breaker is maximum, using conduit and 2/O THHN aluminum wire, 145 double breaker is maximum.

You are aware that the secondary panelboard in the garage needs to have its own grounding system. The Neutral bus cannot be bounded to the secondary panelboard.

That means you need to install a primary and secondary ground rods to ground the panelboard to. Because the garage is a remote structure it has to have its own grounding and bonding system.

Depends on the wiring and load. Water heaters pull a lot of amps. Either way you get the same protection since the 50's are bridged. Just use the best quality breakers and a good ground source.

That is completely incorrect.