Easiest way is mixed entity units. Create two types of soldiers in ebsp (or just one additional) - one with Kar98s, second with MP40s. Then in sbps find your squad and edit squad_loadout. There should be one type of soldiers with their number in squad, for example 4x grenadiers in Grenadier squad. Now just lower number of grenadiers and add your soldiers.
This is how it's done in Assault Grenadiers squad - there are four grenadiers and one Panzergrenadier (leader). Look this squad up in editor to get an idea how it works.
Thank you so much for answering! It solved my issue.
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