Isomerization of normal paraffins to form branched paraffins may be complicated by significant cracking of C7+ paraffins under isomerization reaction conditions. This issue may complicate upgrading of hydrocarbon feeds having significant quantities of heavier normal paraffins. Cracking selectivity may be decreased by combining one or more naphthenic compounds with a feed mixture comprising at least one C7+ normal paraffin and/or by utilizing tungstated zirconium catalysts having decreased tungsten loading. Further, C5 and C6 normal paraffins may undergo isomerization in the presence of C7+ normal paraffins. Methods for isomerizing normal paraffins may comprise: providing a feed mixture comprising at least C5-C7 normal paraffins and lacking normal paraffins larger than C8; and contacting the feed mixture with a bifunctional mixed metal oxide catalyst under isomerization reaction conditions effective to form a product mixture comprising one or more branched paraffins formed from each of the C5-C7 normal paraffins.