Is it possible to put sealant on the front 4 teeth if they are weak and chipping?

Weakened teeth: First determine what is causing the weakening so it doesn't happen again. Then there are options like bonding, veneers or sometimes crowns if badly damaged, that can be used to replace, repair and protect the tooth, with an excellent, long lasting, conservative and esthetic result. See a qualified cosmetic dentist for all your repair options and preventitive measures.

Placement of sealant: Generally the placement of a sealant in the traditional sense is on posterior teeth on the occlusal(biting) surface down in the grooves. This is usually done as a preventive measure to prevent decay, helps keep bacteria from settling into areas that cannot be cleaned. Sealants are not meant as a fix for chipping teeth and I have never seen them placed on front teeth.

Not 4 that purpose: Sealants are meant as a preventive measure to seal pits and fissures, mostly on back teeth to prevent those areas from forming cavities. If your teeth are weak and chipping, something more substantial would be necessary to treat\fix\strengthen those teeth. See your dentist to explore your treatment options and what would be best in your particular case.

Yes, but no: Sealants can be placed on front teeth, but usually is done on the backs if there are deep pits. It is not strong enough to strengthen thin enamel.