The decision to reopen inquests into the 21 deaths helps the families' quest for truth, said Kevin Winters.
But it means they will experience a re-traumatising process, added the lawyer for five of the families.
Senior coroner Louise Hunt said on Wednesday new hearings would be held into the bombings in November 1974, believed to have been by the IRA.
Twenty one people died and 222 were injured when bombs went off in the Mulberry Bush and Tavern in the Town pubs.
Q&A: Pub bombings inquests
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Six men were wrongly convicted for the attacks and spent 16 years in jail before their acquittals.
Inquests were opened days after the atrocity but were not continued after the men were jailed.
Mr Winters, senior partner at KRW Law LLP, said Wednesday's decision was a "significant and poignant day" for all involved.
But he said the "severely traumatised" families who had been fighting for new inquests now faced hearing some potentially uncomfortable evidence.
"The actual campaign process, the fight for justice, the fight for truth, the fight to get some sort of conduit to expose and put out into the open what actually happened - that is a re-traumatising process for many families," he said.
"Yesterday was a massively emotional occasion... so there's a lot of difficult days ahead... but, if I could put it like this, they are welcome difficulties and that is what the families and us on their behalf will embrace."
In confirming new inquests would be held, Ms Hunt said there was a "wealth of evidence that still has not been heard" about the attacks.
A hearing in Solihull was told there was evidence police had missed two potential warnings of the bomb attacks.
But West Midlands Police maintained there was "simply no evidential basis" for reopening the inquests and argued the coroner did not have the jurisdiction to hear the inquests, something Ms Hunt rejected.
The families, who have campaigned for many years for new hearings, said they were overwhelmed by the decision to help them get "truth, justice and accountability".
A preliminary hearing will be held later this year and it is thought full inquests will happen in 2017.
There are "difficult days ahead" for the families of the Birmingham pub bombing victims, according to a lawyer.