I discovered through Ancestry.com that their father died in 1858 in Greene County Arkansas, so I assume that HF and LH Tennison were initally in the 13th Arkansas Regiment. Family lore has it that the brothers were in cavalry units and came west with a group of CS cavalry veterans after the war (Levi lived in Seattle, where I reside, and died in California in 1915). I found a site which stated that the 30th was later mounted so this this makes sense.
Thanks again,
JT