IRT your frogs; would ensure enclosures are as stress free as possible and the temperature/humidity parameters are spot on. Not all frogs respond positively to off-tank feeding or tong feeding; which could introduce additional stressors. A stressed out frog can reduce or stop feeding and it is also normal for frogs to slow down their metabolism during Winter. Although some animals do require at times force feeding; think it should only be used as a last resort when animal is loosing weight. Good luck !