1) What are you talking about - the L-D sequence will only load into halftracks of the same platoon (deliberately).
The only other auto load is the "load all" key for everybody, which works the same way as the AI routine, for those who want to do such. WRT tank riders - it will leave some/most on foot as that is realistic. Apart from the USSR tank riding was uncommon (as they were highly vulnerable when doing so). Plus - the AI now knows about that, and will plink off TRs with MG, rifles etc - tanks are not the "super APC" they were i SP1/2/3.
Otherwise - you need to load things into vehicles individually.
2) As to the brandenbergers - the OOB designer obviously assigned the wrong type of halftrack. The weapons support ones do not have a section lift capacity. (and why we even have such an oddity in the OOB is beyond me, since that one would be even rarer than hen's teeth in the first place

!
Cheers
Andy