I have 2 TB48 (5700mAh) intelligent flight battery. Charging 40+ times. Currently the power of these batteries shown 4500 and 4700mAh respectively. Is it normal/safe to fly? Is it means the lifespan for these batteries going to be ended?

You can expect a drop-off in available power as the battery is recharged. Have you carried out the recommended resetting every 15-20 charges? This will recover some of the maximum specified power but not all. You need to charge to 100% and discharge in one continuous discharge to at least 5% or less or until the power cuts out. This can involve some careful low level hovering and keeping the throttle slightly up once landed. The important thing is that it is uninterrupted.