Well, a number of Yukkuri fight with sticks held in their mouths. Bodied Yukkuri have hands, so it's a natural progression - though i severely doubt they'd be able to hold anything too heavy.
Flandre has a spear. Since Papa's an advanced type, it may well be one of Flan's Accessories. As for weapons, a regular bodied yukkuri should be able to fire a single-shot 9mm without obliterating its fingers, but anything with more punch or greater rate of fire would probably cause their hands or arms to suffer damage.
Well, these are different from the widely accepted Flan-type, they even appear to have some sliver of intelligence...so this is acceptable. Flan-types usually carry sticks, too (Laevatei~n!) so yeah.