You still haven't said what the exposure level was nor the duration (you weren't in there for 3 straight years, you came out). Also, be careful about drawing causality conclusions based on 4 individuals and current medical condition. You will have to prove a case and the odds are stacked against proving lead over exposure.
Chronic lead exposure (toxicity) would have manifested in a lot of other severe symptoms at the time of exposure. You would need blood test levels and bone x-rays to confirm excess exposure that exceeded the Federal permissible blood level at the time. The current biological exposure index (a level that should not be exceeded) for lead-exposed workers in the U.S. is 30 µg/dL in a random blood specimen. The lead in your blood and soft tissues from any exposure then is long gone now and unlikely any remains in your bones.
Further, the effects of lead toxicity in adults is on the peripheral nervous system not the central nervous system (neurological). Lastly, lead toxicity has been well studied and has a long history of extensive documentation. Seizures as a result of either acute or chronic lead poisoning only happens (rarely) when blood levels are very high, not years later after the exposure has ended.
I'm not saying that it isn't somehow related, just that you are going to have a very difficult time proving it. The science and study of lead toxicity isn't on your side.