If hand weeding is not possible, spraying path weeder is a safe and effective way to control weeds growing between pavers. Just follow the directions on the label to apply.
Some community members have also had success simply using boiling water, but please take care and use personal protective equipment such as enclosed footwear and gloves.
To minimise gaps between pavers, use paving sand. Sand is the appropriate product as it caters for movement of the pavers. If you were to use a cement-based product, it could crack.
I recommend a product like Dingo 20kg Powerloc Paving Sand which is flexible in nature and a polymer-based product that is resistant to weed growth. You can see Bunnings Workshop community member @TimD use this product in his How to repair an old brick path discussion. - MitchellMc
