You’re saying bar, but to clarify are you hoping to also do food? I’d make a reservation if possible, there’s realistically no other way to guarantee a high top area that seats 8-10 people.

Foundry on Elm has an area that would fit your needs. Bright inside and nice - easy parking, Easy access from the redline

From the same restaurant group could reach out to the independent in union square and see if you could use their bar/lounge space on the left side. I don’t think they typically open that side up until the evening, but not 100% sure. - that time of day should have reasonable parking and is easy access from green line

Olde Magoons saloon in Magoun square may not take reservations but you could contact ahead of time. Cozy Irish pub vibes with a slightly confusing menu, but good food and solid beer list. Easy parking and on the green line

Honorable mentions: five horses in Davis square, Russell house tavern in Harvard sq, Za in Kendall square (and they have an email request form you can use)