If it must be those two T pieces then 2 olives, 2 nuts and a short length of copper (ie the manufacturers approved fittings) Anything else is a botch. If you want them tight together the best leak-proof botch might be a brass coupling with no sealant and then silver soldering the joints to seal them.
The locktite is really only any good if you can torque up the joint while it sets - these, being parallel threads will only torque up when they bottom out.
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