Were the OUIs felony's or misdemeanors?
If the OUI was a conviction (not a CWOF, which is common for a first offense), in MA, and after May 27, 1994, it's a misdemeanor punishable by up to 2 1/2 years, which means makes one a federally prohibited person even though it is not classified as a felony.
The ONLY remedy is to have the conviction set aside or a pardon. Pardon is a tough route, since the pardon application specifically asks if you are seeking restoration of firearms rights (you won't "slide one through" and get firearms rights restored without answering yes). The governor and his advisors are going to be reluctant to issue pardons in general; more reluctant to issue one restoring firearms rights to a DUI convict; and even more reluctant to one that would allow the applicant "first time offender" treatment on any subsequent DUI; and that's before the gov's advisors look at the fact you did it twice.
You need top flight legal counsel who is familiar with DUI law, the pardon process and procedures for appealing or setting aside old convictions (harder in MA than in many other states). You also need an attorney with enough integrity to be direct with your chances, and not run up thousands in legal bills on a longshot without telling you honestly what your odds of success are. Langer and Cohen will both meet that criteria but, like most things in life, thou gettuth what thou payuth for and these folks do not come cheap (except for the initial office consult).
Also, as a first step, you will need to find out which, if any, of the convictions are after the May 27, 1994 deadline - and thus the "problem ones" from the federal perspective. It is not likely to come cheap, nor is it the kind of "for the public good" case an attorney is likely to take pro bono.
Do not screw with the federal prohibition - the feds routinely go after prison time when they encounter such offenders, even for something as simple as possession of ammunition or renting a gun for temporary use at a firing range.
I just don't see how they can hold back my second amendment right due to something that happened in the past and has nothing to do with firearms.
For the same reason dogs lick their private parts (because they can).
The "Felon or 2 year" provision traps a lot of people in MA as 2.5 years is a very common maximum sentence for many crimes that almost never carry an actual sentence close to that. It's the result of legislative posturing - expect the 2 1/2 to increase 3 3 the next time someone feels the need to show they are tough on OUI.