How much meat should I serve per person?

About 8oz or 225g/person is probably a good place to start.

Think about when you have a standard steak or a piece of chicken in a restaurant. The pre-cooked weight will usually be in the region of 8-10oz.

A good rule of thumb is to allow 1lb of meat (before cooking) per person, not counting small children who will obviously eat less. It's better to have too much than not enough - you can always use leftovers.

It depends in part who you are serving--hungry college students (or those with that mindset) eat considerably more free food than do wealthy health-conscious professionals. You also need to keep in mind that while you don't want to overshoot massively, it also looks bad to run out of food. You may also need to keep in mind that a significant number of people do not eat pork for personal/religious reasons, so you want to not run too short of other options.

That said, the best way to estimate is to see what people who do this all the time provide. For instance, CityBBQ provides 8 lbs of meat for 20-24 people. Famous Dave's seems to offer about 8 lbs also, if you can count their 60 chicken wings as equivalent to your lasagna. (This is likely cooked weight, though neither site says.)

For entertaining purposes the rule of thumb I've most commonly seen in your case, where the meat is the primary food being served, is about 8-10 ounces per person. That's size per portion after cooking. You are making pulled pork and brisket, and each of those will lose just over 40% of their weight during cooking. So if you assume 5 ounces of brisket and 5 ounces of pork per person, that's about 8.3 ounces of each meat pre-cooked per person.

So you'd probably want (number of meat eaters times 8.3) divided by 16 pounds of each meat type, plus or minus any fudge factor you wish to include.

In the past, when I host a party at home and I serve Buffet style with sides, Rice, Potatoes, Mc & Cheese, Salad and veggies, I end up with about 2oz of beef, whether is flank, tenderloin, etc per person. Remember, you have appetizers as well before the main and I serve, Garlic Shrimp, plus an assortment of dips & chips.

Depending on where you live, your local government food or health departments will publish a food guide or food pyramid

In many western countries that eat red meats, you will find this showing about 120 g (4 oz) of red meat, about the size of a pack of cards or a typical hamburger patie

At many functions and restaurants the host will serve more than this, this is marketing, not love

In the case of pulled pork, a generous tong load into an open roll is about 50 to 60 g (2 oz). I did a 50+ person event recently, and there was only about 1.2 pulled pork rolls per person consumed. Pulled pork loses nearly half it's weight from raw to cooked. See https://cooking.stackexchange.com/a/57059/3203

For brisket, the loss is less (depending on beef type). And again about 50 to 60 g is a roll full, especially by the time you add some coleslaw, sauerkraut etc.

So even with if everyone has a brisket and a pork roll, you are still at 120 g cooked, or 240 g (8 oz) raw. Always over cater, as you never know who is going to turn up, and pulled pork makes great left overs

I have grilled, barbecued, smoked brisket whole my life. I would say you´ll actually need about 2 pounds/person. This is because as this homepage also tells, http://goodporkbadpork.com/how-much-brisket-per-person/ the brisket will lose about 40% if you plan on trimming it!