Yes, you can combine them. I would follow the recipe for the fruit you use the most of. If equal amounts, read both sets of ingredients and keep the ratios the same.
With the fruits you listed, you shouldn't have any problems as they all set well.
Jam is low risk if proper canning methods are used. The worst that can happen is that it doesn't set (then we call it syrup), or it sets too firmly (heat and use as a glaze or still as jam).

Deanna

Thanks so much, I did go ahead and make the strawberry-rasp jam but do have intentions to make a few combos in the near future. The strawberry/rasp jam was the best I've ever made and definitely delish. Lori

You could always try Old Bachelor's Jam. There are many versions, some with liqueur and some not. This one from Martha Stewart will give you the basic idea.

Carol

Here is a link that might be useful: Old Bachelor's Jam

raspberry peach is an awesome combination

If you use a low methoxy pectin (Pomona's), any combination of fruit, sugar to taste, whatever you'd like to do, and it will set perfectly. I know because I've done it multiple times, never an issue. Low methoxy pectin does not depend on the sugar to set, so adds far more flexibility.