Jessica Simpson and little sister Ashlee Simpson are both ready for baby No. 3 — and the famous siblings are trying to get pregnant at the same time!

Sources reveal exclusively to Life & Style that Ashlee, 31, was the one who suggested the idea, and Jessica, 36, jumped on board right away.

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"They both think it would be so great to be expecting together,” a friend says. "They keep on talking about how it would be awesome to go through it all together."

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The new additions would join Jessica's two kids with husband Eric Johnson — daughter Maxwell, 4, and three-year-old son Ace. Ashlee is mom to seven-year-old son Bronx with ex Pete Wentz, and 13-month-old daughter Jagger Snow with husband Evan Ross.

However, they might have to convince their hubbies to go along with the plan.

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"Eric and Evan thought they were joking at first, but they’re not,” adds the pal. "They want to both get pregnant this fall."

For more celebrity news, pick up the latest issue of Life & Style, on newsstands now! And for a closer look at Jessica and Ashlee's adorable kids, check out the gallery below.